1026 Int Diploma IB4 v2

Element IB4:

Element IB4:

Monitoring and Measuring

Contents

Contents

Workplace Exposure Limits (WELs)

Workplace Exposure Limits (WELs)

Concept

Concept of of Exposure Exposure Standards Standards 55

Denition

Denition of of Exposure Exposure Limits Limits (EL) (EL) 66

Basis

Basis for for Setting Setting Exposure Exposure Limits Limits 88

Short

Short TTerm erm and and Long Long TTerm erm Exposure Exposure Limits Limits and and Time Time Weighted Weighted Average Average Values Values 1111

Strategies, Methods and Equipment for Sampling and Measuring

Strategies, Methods and Equipment for Sampling and Measuring

Role

Role of of an an Occupational Occupational Hygienist Hygienist 1717

Interpreting

Interpreting a a Hygienist’s Hygienist’s Report Report 1818

Monitoring

Monitoring Strategy Strategy 2020

General

General Methods Methods for for Sampling Sampling and and Analysis oAnalysis of f Respirable Respirable Dust, Dust, Inhalable Inhalable Dust Dust and and Fibres Fibres 2525

Biological Monitoring

Biological Monitoring

Basic

Basic Principles Principles 4242

 Advantage

 Advantages s 4444

Disadvantages 44

Disadvantages 44

Examples

Examples of of the the Use Use of of Biological Biological Monitoring Monitoring 4545

References

Workplace Exposure Limits

(WELs)

Concept of Exposure Standards

Different countries have adopted various frameworks for setting upper permissible concentra tions for airborne substances within the workplace. The rst standard list of exposure limits was put together in the former Soviet Union in the 1930s. In the USA, the ACGIH (American Conference of Governmental and Industrial Hygienists) was formed in 1941 and formed a Threshold Limit Values Committee (TLV). A range of limits was set known as hygiene limits and has been used as the basis for determining limits elsewhere.

The key principle of the ILO Code of Practice “Occupational Exposure to Airborne Substances Harmful to Health”, is the requirement for the employer to protection of workers’ health against the hazards due to the contamination of air at the workplace. The Code also requires each countries competent authority to introduce regulations ‘ on the prevention of contamination’.

Denition of Exposure Limits (EL)

The Glossary Annex of the ILO Code of Practice “Occupational Expos ure to airborne Substances Harmful to Health”, denes the following terms:

Exposure limit to airborne harmful substances at the workplace: concentration in the air of a harmful substance which does not, it is believed in the light of present scientic knowledge, cause adverse health effects—including long-term effects and effects on future generations in workers exposed for eight to ten hours per day and 40 hours per week; such exposure is considered acceptable by the competent authority which establishes the values, although concentrations below the exposure limit may not completely guarantee protection of the health of all workers; the exposure limit therefore does not constitute an absolute dividing line between harmless and harmful concentrations but merely serves as a guide for the prevention of hazards; Exposure limit: other relevant terms:

a. ceiling: indicates a concentration in respiratory air which must not be exceeded at any time;

b. permitted excursion: amount of excursion beyond the time-weighted average which is considered permissible by the competent authority or the body responsible for exposure limits;

c. shortterm exposure: indicates the highest concentration to which workers may be ex -posed for up to 15 minutes without suffering unbearable irritation, chronic or irreversible damage to tissues, or narcosis sufciently pronounced to cause a risk of accidents, reduce their ability to escape in the case of need, or diminish their working efciency, provided that they are not exposed more than a specied number of times during a day and without a specied minimum interval between two successive exposures, and provided that the average daily exposure does not exceed the time-weighted average exposure limit; and d. time-weighted average: average time-weighted concentration which may be adopted as

the exposure limit for substances whose effects are cumulative or for which there is a fairly wide safety margin between concentrations which are harmful and those which are not, provided that the exposure limit for the permitted excursions is not exceeded.

The Annex to the ILO Code of Practice “Ambient Factors in the Workplace”, species that an exposure limit (EL) is a level of exposure which is specied by a competent authority, or some other authoritative organisation such as a professional body, as an indicator of the level to which workers can be exposed without serious injury. It is used as a general term and covers the various expressions employed in national lists, such as “maximum allowable concentration”, “threshold limit value”, “permissible level”, “limit value”, “average limit value”, “permissible limit”, “occupational exposure limit”, “industrial hygiene standards”, etc.

Consequently, any EL represents a risk which is felt to be acceptable, based on a particular criterion and where such limits are given legal status, there is usually an additional requirement to keep exposure as low as practicable rather than simply below the EL.

It is also important to take into account the averaging period for which the limit is intended. Some limits are ceiling values to be continuously applied; others apply to average exposures over a period of up to several years. A short-period limit requires stricter control than a longer-period limit at the same exposure value. For example, a limit applying to a month might allow the exposure to range above the value for days at a time, provided there was a compensating period of low exposure which maintained the monthly average. If the same value were applied to 15-minute averages, the control would have to be good enough to keep every 15-minute average below the value. (See later gures later).

ELs generally limit exposure of the individual, and measurements to be compared with the EL should therefore be taken close to the individual (“personal exposure”), unless the EL in question is clearly stated to be applicable to the general value in the workplace environment. A measurement result sometimes depends on the measurement method, and quality control of measurements is often important.

Some authorities issue lists of values to be used in biological monitoring (analysis of exhaled breath, urine, etc.) or in biological effect monitoring (analysis for metabolites). As with ELs, different lists are derived from different assumptions and are intended to be used in different ways. They include lists of values which are believed to be safe, and values which are not necessarily safe but which represent an acceptable standard of control.

It is the responsibility of the competent authority to specify what ELs should be used, and the responsibility of the employer to obtain this information from the competent authority for any particular hazard and to compare the EL values with exposure levels in workplaces, to verify whether exposure is being properly controlled.

Basis for Setting Exposure Limits

The ILO Code of Practice “Occupational Exposure to Airborne Substances Harmful to Health”, requires that Exposure Limits should be based on a study of the dose-effect and dose response relationship. They should be established in the light of the following data:

a. the physical and chemical properties of the substance, including the nature and quantity of contaminants;

b. the ways in which it is expected to use the substance, and features of the exposure of workers;

c. the results of experiments with laboratory animals designed to establish: i. the acute local and general effects (irritation and sensitisation); ii. the effects of repeated administration; and

iii. the chronic general ef fects, including those affecting the central nervous system (mutagenic, carcinogenic, gonadotropic (affecting the gonads) and teratogenic effects); and

d. the results of:

i. routine medical examinations of exposed workers;

ii. epidemiological investigations; and iii. case studies of occupational diseases.

Testing for setting of EL’s may involve animal experiments in which animals are exposed to increasing concentrations of the substance and the effects are observed and extrapolated to the equivalent human response or as a result of epidemiological study results.

Setting the Level

Whilst the Competent Authorities approach to setting Workplace Exposure Limit’s (WEL’s) may differ, the following principles will be at the core of the decision making process.

First Stage

The rst stage in the level setting process involves an assessment of the toxicology of the substance concerned. The purpose of which is to identify potential harmful human effects and to understand the exposure / response relationship.

In the context of WEL setting, it is important to understand some key points on the exposure/ response curve. These are the ‘No-Observed Adverse Effect Level’ (NOAEL) and the ‘Lowest-Observed Adverse Effect Level’ (LOAEL).

The NOAEL is the highest point on the exposure/response curve at which no adverse health effects are observed; the LOAEL is the lowest point on the exposure-response curve at which adverse health effects are observed. See Figure 1

Second Stage

Having determined the highest ‘no adverse health effects’ level, the next stage is to determine whether this level of exposure is currently being achieved in the workplace. If not, then consideration would be given by the competent authority to the potential for improving existing standards of control so that this level of exposure could be reasonably achieved. If the competent authority considers that this level of exposure is reasonably practicable to achieve by employers, then the WEL will be proposed at this level.

There are a number of substances for which identifying a WEL using a NOAEL or LOAEL is not possible due to the chronic nature of the effects.

For these substances the WEL would be determined by identifying a level of exposure which would represent a standard of control commensurate with good occupational hygiene practice. In determining this level, the severity of the likely health effects, and the cost and efcacy of control solutions would have to be taken into account.

Difculties Associated With Standard Setting

The current exposure limit framework is far from a perfect system; there are a number of problems which should be borne in mind:

▪ The actual doses received by workers may vary due to factors such as work rate which

will cause more air to be inhaled. This is not allowed for in the exposure limit framework; ▪ Chemicals can enter the body by routes other than inhalation, e.g. skin absorption, the

airborne concentration may not be fully indicative of the dose received; ▪ Toxicological data on which limits are based are not necessarily infallible;

▪ Errors in estimating exposures may be signicant; and

▪ Many substances do not have a limit set, which leaves organisations which may have little technical expertise, with the difcult task of setting an ‘in-house’ limit.

Short Term and Long Term Exposure

Limits and Time Weighted Average

Values

Most Workplace Exposure Limits are subject to a LTEL and a STEL, which are time weighted average values.

Short Term Exposure Limit (STEL)

The short term exposure limit is intended to protect workers from acute effects such as:

▪ Excessive irritation;

▪ Irreversible tissue damage; and

▪ Narcosis to the extent that it could impair the worker such that they are more prone to accidents.

The short term exposure limit is a time weighted average exposure typically over 15 minutes

Long Term Exposure Limit (LTEL)

The long term exposure limit is intended to protect workers against chronic effects, to reduce the accumulation of harmful substances in the body that would enhance the risk of disease with continued contact.

The long term exposure limit is a time weighted exposure typically over 8 hours.

The LTEL may be exceeded on occasion if the exposure is for less than 8 hours provided that the STEL is never exceeded.

Units for Short and Long Term Exposure Limits

The limits are expressed in parts per million (ppm) for gases and vapours and milligrams per cubic metre of air (mgm-3_{) for airborne particles, dust, fume, etc.}

Time Weighted Average Value

Workplace Exposure Limits apply to airborne concentrations of substances only. The limits refer to concentrations of hazardous substances in the air averaged over specic time periods known as Time Weighted Averages (TWA). These are LTELs which are averaged over typically 8 hours and STELs averaged over typically 15 minutes.

Figure 2: Time Varying Concentrations

Figure 2 illustrates how the concentration of a hazardous material may vary over time and how this can be compared with an exposure limit. The Time-Weighted Average criteria means that an exposure concentration can be higher than the exposure limit for some of the assessment period, provided that the average concentration remains below the level.

There are no stated maximum exclusions above the TWA level, however the UK’s HSE Guidance Document HSG 173 Monitoring Strategies for Toxic Substances, suggests that exposure excursions greater than one and a half times the exposure limit require urgent attention. Clearly where there is a short-term limit in place as well as a long term limit, this will help to prevent signicant excursions.

The formula for the calculation of 8hr TWA is; 8hr TWA = Σ(C x T)/8

Where Σ is the sum of, C is the average concentration and T is the associated exposure time in hours.

If sampling time is less than the TWA reference period, an extrapolation is made (assuming the sampling period is representative).

8hr TWA = (C x T)/8

If the 8-hour exposure is broken down into results from a number of measurement periods, then the exposure can be calculated as follows:

8hr TWA ₌ (C₁ × T₁) + (C₂ × T₂) + (C₃ × T₃) + .... (C_n × T_n) 8

Example 1

 An operator works for eight hours on a process in which he is exposed to a substance hazardous to health. The average exposure during that period it measured as 0.15mgm -3_.

The 8-hour TWA therefore = C x T = 0.15 x 8

8 8

= 0.15 mgm-3

Example 2

Working periods may be split into several sessions for the purpose of sampling to take account of rest and meal breaks, etc.

Working Period Exposure mgm-3 _{Duration of sampling (hours)}

0800-1030 0.32 2.5

1045 – 1245 0.07 2

1330 – 1530 0.2 2

1545 – 1715 0.1 1.5

Exposure is assumed to be zero during the periods 1030 to 1045, 1245 to 1330 and 1530 to 1545. The 8-hr TWA ₌ (0.32x2.5)+(0x0.25)+(0.07x2)+(0x0.75)+(0.2x2)+(0x0.25)+(0.1x1.5) 8 The 8-hr TWA ₌ 0.80 + 0 + 0.14 + 0 + 0.4 + 0 + 0.15 8 The 8-hr TWA = 0.19 mgm-3 Example 3

Where an operator is exposed to styrene vapours as follows:

▪ For the rst two hours the concentration is 50 ppm.

▪ For the next hour the concentration is 200 ppm; and

▪ For the next 5 hours the concentration is 30 ppm.

Then the 8-hour TWA Exposure ₌ (50 x 2) + (200 x 1) + (30 x 5)

8 = 450/8

= 56.25 ppm

The WEL 8 hour TWA for styrene is 100 ppm (example UK) and therefore exposure is within the limits, however further controls should be considered to further reduce exposure.

Threshold Limit Value (TLV)

The Threshold Limit Value (TLV) has become a generic phrase for the level of a chemical substance which it is believed a worker can be exposed day after day for a working lifetime without adverse health effects.

Similar concepts used in other countries include:

▪ America;

▪ WEEL (Workplace environmental exposure level) created by a committee of the  American Industrial Hygiene Association

▪ Australia;

▪ OES Occupational exposure standard;

▪ France;

▪ VME (Valeur Moyenne d’Exposition);

▪ VLE (Valeur Limite d’Exposition);

▪ Germany;

▪ AGW (Arbeitsplatzgrenzwert trans. Workplace Limit Value);

▪ MAK (Maximale Arbeitsplatz-Konzentration trans. Maximum Workplace

Concentration);

▪ Malaysia;

▪ PEL (Permissible exposure limit);

▪ Netherlands;

▪ MAC (Maximaal Aanvaarde Concentratie trans. Maximum Accepted Concentration);

▪ New Zealand;

▪ WES (Workplace Exposure Standards);

▪ Poland;

▪ NDN (Najwyższe Dopuszczalne Natężenie);

▪ Russia; and

▪ ПДК (предельно допустимая концентрация);

▪ UK.

Permissible Exposure Limits

The Permissible Exposure Limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a substance, usually expressed in parts per million (ppm), or sometimes in milligrams per cubic metre (mg/m3_{). Permissible Exposure Limits are established}

by the Occupational Safety and Health Administration (OSHA).

 A PEL is usually given as a time-weighted average (TWA), although a few limits are Ceiling Limits. A TWA is the average exposure over a specied period of time, usually a nominal eight hours. This means that, for limited periods, a worker may be exposed to concentrations higher than the PEL, so long as the average concentration over eight hours remains lower.

 A Ceiling Limit is one that may not be exceeded, and is applied to irritants and other materials that have immediate effects.

 Approximately 500 PELs have been established, and include amongst others the following substances: ▪ Benzene; ▪ Carbon disulphide; ▪ Chromic acid; ▪ Fluoride as dust; ▪ Formaldehyde; ▪ Hydrogen sulphide; ▪ Mercury; ▪ Styrene; and ▪ Toluene.

Workplace Exposure Limits

In the United Kingdom, TLV’s were originally published as guidance for setting standards. It was however recognised that the UK had different philosophies for managing some chemicals and so a different framework of limits was developed.

HSE guidance note EH40/2005 outlines a Workplace Exposure Limit as;

“WEL’s are occupational exposure limits set under the Control of Substances Hazardous to Health Regulations (COSHH) 2002 (as amended) in order to help protect the health of workers. WEL’s are concentrations of hazardous substances in air, averaged over a specied period of time referred to as a time-weighted average (TWA). (HSE, 2005).”

Table 1: Examples of PEL and WEL’s for Lead and Asbestos

PEL(USA) WEL(UK)

Short Term Long Term Short Term Long Term

Lead n/a lead in air (50 ug/m3_{) n/a 50 μg/dl}

Strategies, Methods and

Equipment for Sampling and

Measuring

Role of an Occupational Hygienist

Occupational hygienists are responsible for identifying, assessing and controlling health hazards in the workplace. They understand how chemical, physical and biological agents may affect the health of the workforce, and in turn the health of the business.

Work activities vary between specialist areas and employers, but may include:

▪ Undertaking workplace surveys, and evaluating situations in the workplace;

▪ Assessing risks to health arising from many different factors, such as chemicals, noise, and poor lighting or ventilation;

▪ Accurately measuring and sampling levels of exposure, often through precise use of specialist equipment;

▪ Accurately recording facts or details of procedures in the workplace;

▪ Eliminating or signicantly reducing risk by facilitating organisational change and by selecting and designing relevant facilities;

▪ Finding cost-effective solutions to risks to health in workplaces of all types, large and small;

▪ Recommending remedies or control methods;

▪ Compiling data, writing reports, and presenting report ndings to clients;

▪ Liaising with a wide range of people, including employers and employees, in the process

of evaluating workplaces;

▪ Considering all options of control (such as ventilation, containment, and personal protective equipment);

▪ Deciding upon or devising the most appropriate solution for specic situations;

▪ Providing clear and accurate information on complex health and safety issues;

▪ Training organisation staff on health and safety issues, such as lead and asbestos

▪ Gaining the condence and cooperation of the workforce;

▪ Persuading company management to develop effective hazard controls when required;

▪ Writing guidance information on health and safety;

▪ Working as part of a team to meet health and safety objectives;

▪ Keeping up to date with scientic and legal developments;

Interpreting a Hygienist’s Report

It is important that the organisation can interpret a hygienists report correctly and understand all the relevant parameters which should be readily checked.

Where a survey of an area, plant or process is conducted, the following should be described: ▪ Area/plant/process surveyed e.g. “a survey of the our transfer area was conducted” ; ▪ Conditions at the time (i.e. personnel, process conditions, risk controls in place) e.g.

“usual operator unavailable”, “shutdown”, ”worst case situation, with no controls”, “as normal, believed to be a representative working day”, “only Blender No 2 was operating”, “protective equipment worn other than overalls” ;

▪ Identify any items examined e.g. “Moreton mixer number 2” ;

▪ Number of employees, duration of shift(s) and task frequency and duration e.g. “7 employees work an 8 hour day, 5 day week with 2 hours overtime worked infrequently”, ”it takes about 30 minutes for 6 bags to be opened and poured daily”;

▪ Diagrams and photographs are useful for clarifying sampling locations and conditions; and

▪ Methods and measurements used in the process.

Where exposure or other measurements are conducted, the following should be included: ▪ Sampling procedures, analytical procedures and relevant technical standard(s) used. If a

relevant published and validated method exists, it should be used in preference to novel method. If it is necessary to use a novel method, a full explanation (including summary of validation) should be provided; and

▪ Locations, times and duration of personal sampling and the names of the individuals concerned. If area/static sampling was also conducted similar details along with the reasons should be provided. e.g. for airborne contaminants “full shift personal sample”, “partial shift area sample”, “grab sample” “as short as practicable (i.e. 5 minute intervals) given analytical constraints”.

Results and Discussion

Results may be presented in the body of the report or as appendices. The level of information, considering the complexity of the processes, tasks and risks, should satisfy the technical reader but not unnecessarily complicate the report.

▪ Results should be traceable to the original eld notes to enable verication of supporting data (e.g. identity of equipment used calibration, etc) should this be needed;

▪ Results of personal sampling should be compared with the relevant exposure standard.

If there is no relevant exposure standard, it will be necessary to either modify or adapt an existing guideline or develop a guideline. The rationale justifying the guideline used should be provided. E.g. for airborne contaminants;

▪ Time Weighted Average (TWA) and Short Term Exposure Limits (STEL),

▪ or TWA and general excursions limits (if no STEL is set),

▪ or long term exposure limits.

▪ Results should be compared with any previous surveys at the premises and data from similar premises if available e.g. “...the process produced results that are similar to other  powder operations” ;

▪ An explanation of general trends and unusual high or low trends should be included; and

▪ The level of risk should be determined (preferably quantitatively) to allow for the adequacy of controls to be assessed and the prioritisation of control options.

Conclusions and Recommendations

Conclusions should be drawn about whether or not the relevant exposure limits have been exceeded and if the work could harm employee health.

Conclusions should also be drawn about adequacy of control and any further practical actions to eliminate or reduce the assessed risk so far as is reasonably practicable.

Recommendations should be selected using the hierarchy of control (personal protective equipment being the last resort) and guidance on an appropriate implementation time frame (e.g. immediate, short, medium or long term) should be provided.

Recommendations arising from regulatory requirements or similar guidelines should reference the relevant source document(s).

 A comprehensible report written in the correct form will make it relatively easy to check that:

▪ The strategy and methods are suitable;

Monitoring Strategy

The following sections describe in more detail the various approaches that can be taken for monitoring. The UK HSE Guidance document HSG 173 provides a good starting point. It outlines a systematic approach to undertaking a survey as illustrated in Figure 3.

Figure 3: Approach to Assessing Hazards to Health by Inhalation Start

Initial appraisal. What are the hazards and risks?

Do you think the exposure is under control?

No

Basic survey

From the initial appraisal and the basic survey decide whether the level of risk is

acceptable

Need more information

Detailed survey

From the monitoring results decide whether the level of

risk is acceptable Routine Monitoring Control of exposure Yes Yes Yes No No

Initial Appraisal

 At rst an initial appraisal of the hazards and risks needs to be undertaken, taking into account all the relevant factors such as:

▪ Substances used;

▪ Physical forms and properties;

▪ Processes involved;

▪ Points of release;

▪ Persons who could be affected;

▪ Work practices;

▪ Means by which substances could be released;

▪ Whether RPE or other forms of PPE is worn and its effectiveness or ergonomic concerns;

and

▪ Relevant Workplace Exposure Limits.

From this information and some qualitative observations a decision can then be made regarding the need for monitoring and if so the type of work to be undertaken.

Basic Survey

This is recommended in HSG 173, although in practice this stage is sometimes missed out or amalgamated with the main full survey as discussed in the following section.

 A basic survey, however, has value in terms of helping to dene the scope of the full survey and ensuring that monitoring resources are effectively targeted at the high risk areas / processes. The approach taken to a basic survey is to select an area which is likely to give a worst case scenario and undertake a quick qualitative or semi-quantitative assessment of exposure using a technique such as a gas stain indicator tube or Tyndall beam to identify the likely exposure.  A more detailed survey can be planned on the basis of the ndings from the initial assessment.

Detailed Survey

Where required, this may use a number of the techniques, qualitative, semi-quantitative and quantitative. Inevitably there will be a balance between the size and extent of the survey and the resources available.

In an ideal world, it would be possible to undertake large numbers of samples over several days, however, as with most health and safety considerations, ‘reasonable practicability’ must be considered.

Before any monitoring is undertaken, it is important that sufcient ‘groundwork’ establishes the situation. The following information should be sought:

▪ Existing risk assessments;

▪ Procedures and workplaces;

▪ Maintenance procedures;

▪ Existing engineering controls and their suitability; ▪ Existing PPE and its suitability;

▪ Previous monitoring results;

▪ Any health surveillance results; and

▪ The extent of information, instructions and training given to staff, including young persons. Further details on undertaking a survey may be found in HSG 173 ‘Monitoring Strategies for  Toxic Substances’ and BS EN 689 ‘Workplace Atmospheres - Guidance for the Assessment of Exposure by Inhalation to Chemical Agents for Comparison with Limit Values and Measurement Strategy’.

Re-appraisal

Monitoring for the basic and detailed surveys may highlight deciencies in control measures and poor work practices.

Where remedial action has been carried out, it is essential to determine that the changes have had a positive effect. This is achieved by a brief reappraisal of the situation.

Routine Monitoring and Factors that Determine

Frequency and Necessity

When it has been decided that the risk to workers has been adequately controlled, it may be required to establish a routine programme to ensure that the control measures stay effective. Routine monitoring can be time-consuming and expensive over the long term. Consequently, if it is suspected that a WEL is not being complied with it can be more cost-effective to invest in better control measures. This reduces the:

▪ Need for expensive routine monitoring; and

▪ Health risks for the workers.

For the results of a routine monitoring programme to be effective in protecting the health of workers, they have to be compared with those obtained from previous monitoring exercises. Considerations include:

▪ The similarity of the processes and tasks monitored;

▪ Where and at what stage of the process the monitoring was carried out; and

▪ The method of collecting and analysing the samples.

The frequency of routine surveys will vary. The nearer the measured exposure is to the WEL the more frequently monitoring will be required.

One scheme for determining the frequency of routine monitoring is given in BS EN 689 “Workplace Atmospheres: Guidance for the Assessment of Exposure by Inhalation to Chemical  Agents for Comparison with Limit Values and Measurement Strategy”.

Importance of Use of Standard Methods

There are a large number of specic guidance documents available from a number of national authorities such as the USA’s National Institute for Occupational Safety and Health (NIOSH) or the UK’s Health and Safety Executive (HSE) who all published detailed sampling methodologies. For example the HSE in a series called ‘Methods for the Determination of Hazardous Substances’, abbreviated to MDHS.

These give details of the sampling as well as the analytical methods used to assess hazardous substances in the atmosphere. Some examples are listed below:

▪ MDHS 14/3: General methods for sampling and gravimetric analysis of respirable and

inhalable dust.

▪ MDHS 70: General methods of sampling airborne gases and vapours.

▪ MDHS 82: The Dust lamp; a simple tool for observing the presence of airborne particles.

Other National standards available include:

▪ Australian Standard 2985 - 2004 - Workplace Atmospheres - Method for sampling and

gravimetric determination of respirable dust; and

▪ USA National Institute for Occupational Safety and Health (NIOSH) Method 7500

Monitoring of Silica, crystalline, by XRD 2003.

 All of these titles are aimed at competent Occupational Hygienists, analytical laboratory technicians, etc. When undertaking monitoring, it is advisable to ensure that the MDHS method is used, where one is available. The results are less likely to be questioned, when evidence is required of compliance with limits, or otherwise, when the monitoring has been undertaken using a recognised method.

Where a specic method is not available, a monitoring protocol should be developed using the professional judgment of competent hygienists in conjunction with laboratory personnel as appropriate. The more general MDHS documents such as MDHS 14/3 and MDHS 70 contain general guidance for such situations.

General Methods for Sampling and

 Analysis of Respirable Dust, Inhalable

Dust and Fibres

 Active Sampling

 Active sampling requires the contaminated breathing atmosphere to be drawn into a sampling device by means of a pump or similar apparatus.

Passive Sampling

Passive air sampling is a method of determining airborne concentrations of substances such volatile contaminants using a passive sampling device (PSD). Instead of using bulky pumps and sorbents, such as charcoal in glass tubes, air samples are collected with a small badge-like device that relies on the diffusion of compounds to a collection surface or sorbent.

Grab Sampling

 Air Sampling can also be divided between ‘Grab sampling’ and ‘Long-term or Time Weighted  Average sampling’.

Grab Sampling, is a technique that enables a single sample to be taken to provide measurement of the concentration of a contaminant in the atmosphere. It is not valid for dusts, although the equivalent is the use of a dust lamp or a measurement using a light scatter direct reading instrument.

The main application for this type of technique is as part of a basic survey or quick check to see whether there is a problem or not.

Time Weighted Average (Long-Term) Sampling

Long-term in this context does not necessarily refer to a long time period, but unlike grab sampling which just measures an instantaneous concentration, long-term sampling enables a ‘Time-Weighted Average’ (TWA) concentration to be determined, which could be based on a few minutes of sampling or several days.

This is in many respects of greater relevance when comparing against occupational hygiene standards since these are expressed as TWAs.

These methods can be further divided in terms of direct reading and indirect reading, although only the latter is valid for gravimetric technique involving dust. Both types are available for some applications as personal sampling or static sampling equipment.

Calculation of 8 Hour Equivalent TWA Exposures

Where a material has a known Workplace Exposure Limit, a calculated TWA exposure can be used as a direct comparison.

Where a gravimetric or an absorbed sample is collected, a calculation needs to be performed to obtain the TWA exposure.

For example, a sampler is set to 2 litres per minute (0.002 m3_{/min) and the atmosphere is}

sampled for Cadmium dust for 2 hours. The laboratory identies that 0.09 mg of cadmium was collected. The TWA exposure could then be calculated as follows:

Sample volume = ow rate of pump X sample time

Concentration = Mass of sample collected/sample volume mg/m3

The Sample time must be in the same units as used in the sampler ow rate, e.g. minutes. Therefore:

Sample volume = 0.002m3_{/min X (2x60mins) = 0.002 X 120 = 0.24m}3

Concentration = 0.09mg / 0.24m3 _{= 0.375 mg/m}3

2 hour TWA = Concentration X Time / Av Time Period

= (0.375 X 2) / 2 = 0.375 mg/m3

If a separate test indicated that a TWA exposure for cadmium for the next three hours was 0.2 mg/m3 _{but no more exposure took place that day, an 8-hour TWA may be calculated as follows:}

8-hour TWA ₌ (0.375 x 2) + (0.2 x 3)

8

8-hour TWA = 0.169 mgm-3

This should then be compared with the WEL for Cadmium, which for example in the UK is 0.025 mg/m3

If the determined 8 hour equivalent TWA is greater than the assigned WEL, control measures must be improved to reduce the 8 hour equivalent TWA to below the assigned WEL.

If the determined 8 hour equivalent TWA is of the same order as the assigned TWA, further monitoring may be required, but additional control measures will still be required to ensure the assigned WEL is not exceeded.

If the determined 8 hour equivalent is below the assigned WEL, routine monitoring will be required to ensure the continuing efciency of the control measures.

Worked Example

 A worker in a bakery is exposed to our dust as indicated in the following table. The data is collected following gravimetric sampling and is given in table 2;

Table 2: Results of Sampling Working Period

Total shift time = 8 hours

Tasks undertaken by bakery operative

Exposure to our dust (mg/m3)

0800-1030 Weighing ingredients 14

1030-1045 Break

1045-1245 Charging the mixers 10

1245-1345 Lunch

1345-1545 Cleaning equipment 2.5

1545-1600  Assisting maintenance staff 0 (assumed)

 Assuming that exposure is zero during break and lunch times the 8 hour TWA can be calculated as follows:

Using the equation: TWA = Σ(C x t) / 8

TWA = ((14 x 2.5) + (10 x 2) + (2.5 x 2)) / 8 TWA = (35 + 20 + 5) / 8

TWA = 60 / 8

TWA = 7.5 mg/m3

This gure can now be compared to the WEL specied in EH40, 10 mg/m3

Should the circumstances of the work change, e.g. the bakery changes the work patterns such that the operative now only charges the mixer and the shift is extended to 10 hours with a 1 hour break, the TWA would need to be recalculated. This can be done as follows:

Using the equation: TWA = Σ(C x t) / 8 TWA = (10 x 9) / 8 TWA = 90 / 8

TWA = 11.25 mg/m3

Sampling for Dusts

Sampling of respirable and inhalable dust can be by personal and / or static (area) sampling and can be undertaken as a part of a monitoring regime.

For both respirable and inhalable dust, active sampling is used. This is where the contaminant is pumped through a suitable lter which provides a sample for laboratory analysis (indirect reading).

To differentiate between respirable and inhalable dust, different samplers are used which work on separating the different particle sizes.

Gravimetric analysis involves weighing the dust collected and then relating the weight to the volume of air sampled.

Personal Sampling involves a sampling device being attached to a person, with the sampling head or probe placed, as far as can be realistically achieved, within the operator’s breathing zone, often on the lapel. This device is worn by the operator and should produce a measurement close to the actual exposure of the operator. Thus it is an ideal method for assessing whether a workplace exposure limit has been exceeded.

Disadvantages of personal sampling include the possibility of operator interference. Unless watched continuously, there is a risk that the operators may attempt to manipulate the reading for their own interest. They could seek to lower the result by blocking the inlet, or exaggerate the reading by deliberately standing in a discharge are, or sprinkling dust into the sampling head. Often discussions with the operators prior to sampling can help to gain their full co-operation, and monitoring over an extended period with several different samples can help to eliminate any rogue results. The operator may also inadvertently block the sampler, turn the sampler head to the wrong direction (to face his or her body for example), cause any exible pipes on the sampler to kink or become detached.

Figure 4: Operator Wearing Gravimetric Personal Dust Monitor 

Sample head containing pre-weighed filter 

Tubing

Sample pump set to a known, fixed flow

Ideally, an operator should be watched while wearing a sampler to ensure no interference (intended or otherwise) occurs. The sampling device can then be checked at regular intervals to ensure that it is still operating effectively. This will also give an opportunity for the activity to be observed and any signicant issues noted.

Observation is an important element of monitoring; the assessor’s eyes, ears and nose are important tools.

Static Sampling involves leaving a sampling device in a xed location. It has the advantages of not involving the intrusion of trying to attach a sampling device to a person. Samplers can be located in areas thought to be high in levels of airborne contamination, thus giving a ‘worst case scenario’. Static sampling can also be used on the periphery of hazardous tasks to assess how far the contamination extends, or whether persons not directly involved by the process are affected.

Sampling Equipment

Dusts, fumes, bres etc. are sampled by drawing air through a lter to collect the contaminant, which is then analysed in a laboratory.

The total inhalable dust fraction can be collected and assessed by use of a pre-weighed lter, weighed on an accurate microbalance. This is then placed inside a sample head and attached to a sample pump, with a typical ow rate of 2 litres/minute. The sampling head is selected in accordance with the media being sampled.

There are three inhalable dust sampling heads recommended by MDHS 14/3, which are:

▪ The Institute of Occupational Medicine (IOM) inhalable sampler;

▪ The multi-orice (or seven hole) sampler; and

▪ The conical inhalable sampler (CIS).

The IOM inhalable sampler is usually the preferred method of sampling due to its performance over a range of workplace conditions in compliance with BS EN 481 ‘Workplace atmospheres. Size fraction denitions for measurement of airborne particles.’ 

It is also important that the correct lter medium is selected for the material being assessed. Typically glass bre is the usual medium for gravimetric determinations; however for certain applications silver membrane lters and PVC can be used.

Figure 5: IOM Inhalable Sampler 

Figure 7: Conical Inhalable Sampler 

Following sampling, the lter is carefully removed and then reweighed. Knowing the ow rate of the sample pump, the sample time and the mass change in the lter, the concentration of particulate (mg/m3_{) in the atmosphere sampled can be calculated.}

In addition to measuring total dust, the lter used can be analysed by a suitable technique, for any specic component, e.g. cadmium, nickel, silica. Typical analytical techniques would be atomic absorption spectroscopy or x-ray uorescence.

 A modied device can be used for assessment of the respirable dust fraction of a particulate dust cloud. The respirable fraction is the component of the inhalable dust that passes through to the alveoli. Typically this is composed of particles of less than 10 microns in diameter. These devices consist of a vertical cyclone that spins the air. In the cyclone larger particles are thrown outwards and collected in the grit pot, the respirable fraction being collected on the lter.

Figure 8: Respirable Dust Cyclone Sampler

 Another type of sampler used consists of a horizontal slot, which is of a length, and size that allows particles larger than respirable size to drop out during their journey to the collecting point.

Fibre Sampling

Typically, bre sampling is used for asbestos sampling.

 A measured volume of air is drawn through a membrane lter of mixed esters of cellulose or cellulose nitrate, preferably with square gridlines printed on, although lters without a grid may be used. An open faced lter holder tted with an electrically conducting cylindrical cowl extending between 33 mm and 44 mm in front of the lter, exposing at least 20 mm of the lter, should be used for sampling.

This type of holder is designed to protect the lter, while still permitting uniform deposit.

The cowl points downwards when sampling. A cap is used to protect the lter from contamin ation during transport.

For personal sampling to determine compliance in relation to 4hr control limits the pump ow rate must be 1 litre/min (l/min) and the period of measurement must be representative of worker exposure over a 4hr period.

Prior to removal of an enclosure from which asbest os has been removed or encapsulated, static air monitoring, or clearance indicator sampling (clearance testing), is required. For clearance testing sampling a sample volume of 480 litres for each measurement, with a pump ow rate of between 1 and 16 l/min, is required. The clearance indicator level is currently 0.01 bres per millilitre of air (f/ml).

Figure 9: Cowl Sampler 

There are various other rules governing bre counting which is a specialist activity. Operators need to be trained and then maintain their competence via regular quality assurance schemes in which they count known standard slides.

The World Health Organisation (WHO) recommended method, set out in the publication ‘Determination of airborne bre concentrations. A recommended method, by phase-contrast optical microscopy (membrane lter method)’, WHO Geneva 1997 (ISBN 92 4

 Analysis of Dusts and Fibres

The basic principle for the measurement of dusts and bres is the collection of the dust or bre on a suitable medium, which is then analysed in a laboratory.

For dusts, such analysis may be gravimetric, physical or chemical.

Gravimetric Analysis

Gravimetric analysis relates to weight of material which is trapped on a lter paper from a known volume of air. In practice this means weighing the lter medium prior to sampling and re weighing the lter after sampling, the difference between the two weights can then be considered to be the mass of material from the sampled volume of air. From this information concentration of the airborne mass can be calculated.

Physical Analysis

Physical analysis of dust normally relates to the determination of the particle size and shape. This will normally be done through microscopy and various photographic techniques.

Chemical Analysis

Chemical analysis of dust is carried out to determine the substances within the sample which may be one type or a mixture of different types of dust. For bres, the principal technique for analysis is microscopy.

Microscopy 

 After sampling the lter, which contains the bres, it is treated with a solution of acetone and ‘triacetin’ to make the lter transparent. The bres on a measured area of the lter are counted using phase-contrast optical microscopy (PCM) and the number concentration of bres in the air is calculated.

Not every bre is counted, a statistically signicant number of microscope ‘elds’ (usually bout 0.15%) is viewed and the numbers of bres within a ‘graticule’ viewed through the eyepiece are counted. Only bres of a certain size and shape are counted.

Sampling for Vapours

Sampling for vapours can be by personal and / or static (area) sampling and can be undertaken as a part of a monitoring regime, for which two methods can be used:

▪ Active Sampling, where the contaminant is pumped through a suitable detector, media or

lter, either giving a direct reading or providing a sample for laboratory analysis (indirect reading); and

▪ Passive Sampling, where the contaminant diffuses into a suitable collection media, which either gives an indication of the presence of the contaminant or more commonly is then analysed in a laboratory.

 Active Sampling 

This method relies upon a known volume of air being pumped through a collection medium over a measured time period. Indirect reading instruments provide methods of sampling the atmosphere, which is then analysed in a laboratory to determine the amount of material collected. Various forms of equipment are used depending on the material being sampled. Gases and vapours are sampled by drawing a known quantity of air (by means of a small pump) through an adsorbent or absorbent material, which collects the sample on (adsorb) or in (absorb) the material. It can then be analysed later in a laboratory by using an appropriate analytical technique such as gas chromatography.

 A range of sorbent materials are available, the most common is probably charcoal which is effective in absorbing a range of organic solvents.

Figure 11: Examples of Activated Charcoal Sampling Tubes

 Air is drawn through a sorbent tube relatively slowly, typically at rates of between 50 and 200 ml/minute. If the air passes through too quickly, the component of interest may pass straight through the tube without being absorbed. This does mean however that the technique is not suitable for short term monitoring - if the pump is run for only a few minutes, there is unlikely to be enough material absorbed to analyse. Conversely, if too much material is absorbed the result will not be accurate. To predict whether this has occurred, sorbent tubes usually contain two sections. A section used to collect the sample, separated by a form of porous barrier (e.g. foam) from a smaller section of sorbent, situated downstream of the sample collection area. Should any of the substance being analysed be collected on the smaller section, ‘breakthrough’ is said to have occurred and the result will be an under-estimate and should be discarded. Figure 12: Midget Impinger 

 An alternative method of collecting an airborne sample is by use of an impinger. This is in effect a midget-dreschel bottle containing a liquid through which the atmosphere being sampled is bubbled. The liquid is designed to react with or collect the material for analysis. For example distilled water could be used for acid mist collection.

This is not a popular method and is only used where necessary. It is messy; the content of the impinger can spill out, particularly when used for personal sampling.

Direct Reading Instruments

Direct reading instruments will give a continuous reading of levels of a specic gas or vapour in the atmosphere.

Some of these instruments will provide a print out of the various levels during the sampling period as well as converting the reading to the Time-Weighted Average (TWA), that is the average level over the period sampled. For comparison against the EH40 limits where the sampling period differs from these time periods any resul ts obtained will need to be extrapolated to the relevant reference time period.

Direct reading portable instruments are available for oxygen level, carbon monoxide, hydrogen sulphide, chlorine, and a number of other gases. These instruments are small enough to be carried into conned spaces or can be used as static samplers. Some instruments monitor for more than one of these gases.

Permanent direct reading static sampling equipment is used in some industries. This is more properly dened as ‘Monitoring Equipment’. These will normally give an alarm if certain levels of oxygen or a toxic gas are encountered and do not provide any facility for a direct reading of concentration in air; these are also used for monitoring during work rather than evaluation of levels.

There is a range of direct reading instruments available to indicate the levels of ammable gas or vapour in air, sometimes termed ‘Explosimeters’.

These will either be set for the specic Upper Flammable Limit or Upper Explosive Level (UFL / UEL) and Lower Flammable Level or Lower Explosive Level (LFL / LEL) of the particular gas or vapour, e.g. methane. Explosimeters are usually set to warn at 25% LFL / LEL, or in more sophisticated versions can be set for different levels and will provide direct reading of the percentage of the LFL in air that is present.

Commonly direct reading instruments used in industry include ‘three in one’ or ‘four in one’ multi-gas instruments, which continually measure oxygen level, ammable gas and one or two toxic gases such as carbon monoxide and / or hydrogen sulphide.

This type of instrumentation can be used to monitor atmospheres for work within conned spaces. The safety lamp may be considered a direct reading instrument. This provides a direct indication of oxygen level - ame will reduce or go out in oxygen decient atmospheres and also a direct indication of methane levels by colour, shape and height of ame.

For all direct reading instruments it is important that calibration takes place at regular intervals as recommended by the manufacturer. This is particularly important where the monitoring is for

The advantages of direct reading instruments are:

▪ An instant indication of the level of contamination can be achieved. There is no delay as Laboratory results are awaited;

▪ It is helpful in communication to staff – showing them a direct readout can be reassuring; ▪ The instant readout also makes them useful as a detection (‘sniffer’) device to establish

where the highest concentration of a contaminant may be located. Thus gas leaks or the location of a spill can be located;

▪ They are generally easy to operate; and

▪ A real time variation of exposure over time can be obtained. Data can be downloaded to a spreadsheet and graphs obtained. Peaks in exposure can be viewed and compared with short-term limits.

The main disadvantage of a direct reading instrument is that the reading may not always be accurate, but relies on a detecting mechanism, which will introduce a source of error. This is particularly the case for direct reading dust monitors. For dust, only a gravimetric reading can give a true indication of the exposure level. Thus where reliable data, for legal purposes is required, indirect methods are preferred.

Stain Tube (Colour Metric) Detectors

Stain Tube Detectors are the most common form of Grab Sampling and often used in an emergency situation, e.g. a major spillage.

 A hand pump is used to draw a specic volume of air through a detector tube lled with crystals of a substance, which will react with the gas or vapour being sampled and change colour. The extent of the stain against the scale on the tube will give an indication of the concentration. Figure 13: Stain Detector Tube Pump

The gas or vapour present needs to be identied before this method is used, as the specic tube for the substance must be obtained. There are over 200 tubes available and include oxygen, carbon monoxide, sulphur dioxide, hydrogen sulphide and acetone.

Once a specic tube for the substance is selected, the glass tips at each end of the tube are carefully broken off. The tube is then inserted into the hand pump suction port. The hand pump is then operated, normally in the breathing zone. For each pump stroke the pump bellows is fully compressed and allowed to re-open under internal spring pressure. The required number of compressions of the pump varies depending upon the contaminant. The required number of compressions is manufacturer’s data provided within the tube packaging. An extension tube is

Figure 14: Stain Detector Tubes

The upper stain detector tube, shown in Figure 14, is lled with crystals of a substance that reacts with the contaminant (gas or vapour) being sampled. The crystals change colour in the presence of the contaminant such that the level of contaminant (part per million ppm) can be read directly from the graduated scale.

The lower stain detector tube, shown in Figure 14, is similar, however it contains a liquid reagent in a breakable ampoule rather than being lled with crystals. Breaking the ampoule releases the liquid, which then reacts with the contaminant of interest and the level of contaminant (part per million ppm) can be read directly from the graduated scale.

It is a useful method to provide an initial indication of the concentrations present. It also enables non-technical persons to quickly gain an impression of the concentrations of material present. The following considerations also need to be borne in mind:

▪ The pump must be tested for leaks prior to use by depressing the pump then ensuring it

does not re-inate by covering the inlet;

▪ The tube ends should be sufciently removed to ensure the correct ow rate and the tube

must be correctly inserted to prevent bypass leakage;

▪ The pump bellows must be fully depressed on each stroke, ensuring that the correct number of strokes are used;

▪ The reading is a ‘snapshot’ at the time of measurement and may not be truly representative; ▪ The colour changes are not always sharp and clear, so may be difcult to read off;

Passive Sampling 

The indirect methods mentioned above rely on a known volume of air being pumped through a collection medium. Passive sampling relies on the material of interest diffusing into the collecting medium, which may either be a tube or badge.

The badge has a at permeable membrane supported over a shallow layer of sorbent. The tube type sampler has a smaller permeable membrane supported over a deep metal tube lled with an absorbent.

 Alternatively, a glass tube open at each end with a porous membrane can be used.

The contaminant diffuses through the sample medium at a calculated rate. When sampling is completed, the tubes are returned to the laboratory for analysis in the same way as for a pumped sorbent tube.

Thus knowing the exposure time, a TWA concentration can be calculated. Sampling starts when the ends of the tube or cover in the case of a badge are removed.

The advantage of this method is that no pump is required and the sampler can be left for several days or weeks if necessary. Personal sampling is much easier too, with no pumps and tubing to encumber the operator.

There is however some doubt regarding the accuracy of the method. The scientic community seems divided on the issue. One view is that without knowing a precise volume sampled there is probably more margin for error, particularly with factors such as wind speed affecting the amount of material absorbed onto the lter.

This method is particularly effective for long-term sampling, e.g. nitrous oxide gasses in a workplace over several days or weeks.

 Analysis of Vapours

Many of the methods discussed involve a laboratory to undertake analysis of the sample. The laboratory may be a part of the same organisation as the person taking the samples, or independent. The relation between the hygienist (sample taker) and the analysts (persons undertaking the laboratory analysis) is an important one and generally works best where the same partnership is used regularly. It is generally advisable to hold discussions with the laboratory prior to sampling to ensure that:

▪ Samples are being collected on the correct medium;

▪ The laboratory is able to undertake the analysis;

▪ The analysis can be performed by a recognised MDHS method;

▪ The laboratory can undertake the work quickly enough to satisfy the client; and

▪ An appropriate sample time is being used. The laboratory would probably advise that sampling an organic solvent for ve minutes would not collect sufcient material to allow detection. They may also advise where, ‘break through’ or lter overloading could occur due to too much sample, and therefore suggest the sampling time be split, or a lower ow rate be adopted for the pump.

Spectroscopy 

Spectroscopy is the study of the interaction between radiation and matter as a function of wavelength.

Spectroscopy/spectrometry is often used in physical and analytical chemistry for the identication of substances through the spectrum emitted from or absorbed by them.

There are different types of spectroscopy/spectrometry.

Mass Spectrometry

Sample molecules are ionised by high energy electrons. The mass to charge ratio of these ions is measured very accurately by electrostatic acceleration and magnetic eld perturbation, providing a precise molecular weight.

Chromatography 

Chromatography is a method for separating the constituents of a solution (gas or liquid) by exploiting the different bonding properties of different molecules.

Used in qualitative and quantitative analysis of biological and chemical substances, this technique employs two immiscible substances. One substance (a gas or liquid, called the mobile phase) transports the solution being analysed through the other substance (a liquid or solid, called the stationary phase).

Biological Monitoring

Biological monitoring is the term given to techniques used for estimating the exposure of a worker to a hazardous substance by examining the biological systems and/or metabolites in the body.

Types of monitoring can include:

▪ Blood tests;

▪ Urine tests;

▪ Skin prick tests (to determine allergic reactions), also sometimes referred to as ‘challenge testing’;

▪ Exhaled breath monitoring; and

▪ Analysis of hair, nails, etc. (less common).

Basic Principles

Biological monitoring provides one means to assess exposure and health risk to workers. It entails measurement of the concentration of a chemical determinant in the biological media of those exposed and is an indicator of the uptake of a substance, expressed on the form of a Biological Limit Value (BLV).

Biological Monitoring Guidance Values are either based on:

▪ A relationship between biological concentrations and health effects;

▪ A relationship between biological concentrations and exposure at the level of the WEL or  ▪ Data collected from a representative sample of workplaces correctly applying the principles

of good occupational hygiene practice.

BMGVs are set where they are likely to be of practical value, suitable monitoring methods exist and there is sufcient data available.

In the United States, Biological Exposure Indices (BEIs) are an example of BLVs for assessing biological monitoring results. Similar standards exist in the UK in the form of Biological Monitoring Guidance Values (BMGV).

BEIs represent the levels of determinants that are most likely to be observed in specimens collected from healthy workers who have been exposed to chemicals to the same extent as workers with inhalation exposure at the Threshold Limit Value

(TLV).

The exceptions are the BEIs for chemicals for which the TLVs are based on protection against nonsystemic effects (e.g., irritation or respiratory impairment) where biological monitoring is desirable because of the potential for signicant absorption via an additional route of entry (usually the skin).

Biological monitoring indirectly reects the dose to a worker from exposure to the chemical of interest. The BEI generally indicates a concentration below which nearly all workers should not experience adverse health effects. The BEI determinant can be the chemical itself; one or more metabolites; or a characteristic, reversible biochemical change induced by the chemical. The BEIs are not intended for use as a measure of adverse effects or for diagnosis of occupational illness.

Biological monitoring can assist the occupational health professional to detect and determine absorption via the skin or gastrointestinal system. In addition to that by inhalation;

▪ Assess body burden;

▪ Reconstruct past exposure in the absence of other exposure measurements;

▪ Detect non occupational exposure among workers;

▪ Test the efcacy of personal protective equipment and engineering controls; and

▪ Monitor work practices.

Biological monitoring serves as a complement to exposure assessment by air sampling. The existence of a BEI does not indicate a need to conduct biological monitoring. Conducting, designing, and interpreting biological monitoring protocols and the application of the BEI requires professional experience in occupational health and reference to the current edition of the Documentation of the Threshold Limit Values and Biological Exposure Indices (ACGIH). Section 4 of the ILO Code of Practice: Occupational Exposure to Airborne Substances Harmful to Health sets out the principle that:

‘Whenever valid biological monitoring methods are available, they should be used to complement monitoring of the working environment in order to increase protection of workers’ health.’  If a result exceeds the Biological Limit Value (BLV), it does not necessarily mean that ill-health will result; however it does indicate control measures may not be adequate and more could be achieved.

The advantage of BLVs is that they provide an accurate estimation of the actual exposure and therefore a denitive indication of whether control measures are effective.

 Advantages

BLVs are set where they are likely to be of practical value, suitable monitoring methods exist and there is sufcient data available. The advantages of this approach are:

▪ It can be a very useful complementary technique to air monitoring when air sampling techniques alone may not give a reliable indication of exposure;

▪ It provides an accurate estimation of the actual exposure and therefore a denitive indication of whether control measures are effective.

▪ The overall exposure results are from all routes, i.e. inhalation, ingestion, absorption and injection; and

▪ The exposure does not need to have been observed, thus can be used where air monitoring

is not practicable. It is also effective for monitoring intake of illegal substances.

Disadvantages

The disadvantages of biological monitoring, however, are:

▪ It can be expensive – requiring occupational health and laboratory resources. ▪ A number of external factors may affect the results:

▪ individual differences in metabolism; ▪ health status of the individual; and

▪ when the sample is taken.

▪ It is by nature a reactive form of monitoring i.e. if an excessive concentration of material is found within the worker’s body, it is too late – the harmful exposure has already occurred;

▪ It can be invasive and staff may be uncomfortable with giving samples; and

▪ Only a certain number of substances can be monitored in this way.

BLVs are not an alternative or replacement for airborne exposure limits. BLVs are generally non-statutory and any biological monitoring undertaken in association with a guidance value needs to be conducted on a voluntary basis (i.e. with the fully informed consent of all concerned). Monitoring may need to be carried out at a specic time, e.g. immediately post-shift.

This is because some substances will be quickly metabolised. Alcohol for example, is metabolised at approximately one unit per hour; thus the testing needs to be undertaken as soon as possible.

Examples of the Use of Biological

Monitoring

Biological monitoring is often used for a range of chemicals and substances such as:

▪ Styrene;

▪ Heavy metals such as Lead, Cadmium Mercury and Cobalt;

▪ Lindane (used in timer treatment);

▪ 4,4 methylenebis-(2-chloroaniline) (MbOCA); and

▪ 4,4 -methylenedianiline (MDA).

Sometimes the substance itself is monitored, or sometimes a metabolite is measured. For example, to monitor for styrene, mandelic acid is measured in urine.

This is because styrene undergoes a chemical change in the body or metabolises to produce mandelic acid.

Some BLVs are cited as an amount of material per amount of creatinine in urine. For example in the UK, MbOCA used in the manufacture of dense plastics, e.g shopping trolley wheels, has a BMGV of 15 μmol total MbOCA per mol of creatinine in urine. Creatinine is a protein which is excreted at a steady rate by the body, thus is a means of normalising for uctuations of dilution rates of urine, i.e. when a person has drunk a lot of water, materials dissolved in the urine will be more dilute and thus the concentration of material being analysed will be lower.

Section 4 of the ILO Code of Practice: Occupational Exposure to Airborne Substances Harmful to Health identies the following principles supporting any biological monitoring regime;

▪ Evaluation of the over-all hazard presented by the working environment should be based

on the results from the group of workers exposed to a given level of the harmful substance, in order to offset the effect of individual biological variability;

▪ Any worker for whom the ndings exceed the biological limits should undergo further and

repeated biological and medical investigations;

▪ The results of medical examinations and biological monitoring should be made available

to the worker, and at his request to his personal physician;

▪ The medical surveillance provided should normally be carried out in working hours and should be free of cost to the worker;

▪ Provision should be made for the maintenance, for an appropriate period of time, of records of medical and biological examinations and of occupational exposure. These records should be available for prospective epidemiological and other research. The records should permit subsequent medical surveillance of workers after cessation of employment; and