1026 Int Diploma IB3 v2

Hazardous Substances and

Hazardous Substances and

Other Chemicals –

Other Chemicals –

Engineering

Engineering

Controls and Personal

Controls and Personal

Protective Equipment

Contents

Contents

Ventilation

Ventilation

55

Dilution

Dilution Ventilation Ventilation (General (General Ventilation) Ventilation) 55

Local Exhaust Ventilation (LEV)

Local Exhaust Ventilation (LEV)

66

 Assessing the Pe

 Assessing the Performance rformance of LEV of LEV 2020

Personal Protective Equipment

Personal Protective Equipment

2727

Respiratory

Respiratory Protective Protective Equipment Equipment (RPE) (RPE) 2727 Skin

Skin Protection Protection 3939

Eye

Eye Protection Protection 4242

Training 44 Training 44 Maintenance 44 Maintenance 44

Conclusions

Conclusions

4545

References

References

4646

Ventilation

Ventilation in workplaces can include both general (fresh air) ventilation, for the comfort of workers, and ventilation used to control airborne contamination of the workplace. This Element relates to the latter.

Ventilation used to control airborne contamination can be either dilution ventilation or local exhaust ventilation (LEV).

Dilution ventilation provides a ow of air into and out of the working area and does not give any control at the source of the contaminant. The background concentration is reduced by the addition of fresh air.

LEV intercepts the contaminant as soon as it is generated and directs it into a system of ducting connected to an extraction fan. To achieve the same degree of control, far less air is extracted with an LEV system than with an equivalent dilution system, with considerable cost savings.

Dilution Ventilation (General

Ventilation)

For relatively low risk situations involving small quantities of material or relatively low hazard substances, it may be sufcient to provide good dilution (general) ventilation within the workplace. This can either be natural involving windows and other openings, or more usually in a workplace by forced extraction.

Natural ventilation through opened windows, doors and wall vents allows fresh air to enter an area resulting in a diluting effect on airborne contaminants but has limited control. The use of fans to deliver and remove air to and from an area provides dilution ventilation and can achieve the required air changes in the room.

Figure 1: General Ventilation

Use can be made of physical properties associated with processes to bring about ventilation, for example hot processes will result in contaminants rising with the heat and can be directed into a ue to exhaust to atmosphere.

Local Exhaust Ventilation (LEV)

Local exhaust ventilation (LEV) is a method of reducing workers’ exposure to potentially harmful substances generated by the work process. The LEV deals with the contaminant at, or close to the point of release, reducing the potential for exposure to the substance.

 A typical local exhaust ventilation system will extract air using a hood, partial enclosure or other opening and transport the contaminated air away from the workplace, cleaning it and then discharging it either outside or back into the workplace.

LEV can be used to control a wide range of substances including gases and vapours, fume and solids.

Table 1: Common Processes and Sources

Process Examples Creation

mechanism(s) and source description Form of contaminant Possible Controls Rotating tools and parts

Orbital, belt and disc sanders. Disc cutters. Circular saws and routers.

Lathes. Drills.

 Abrasive wheels.

Rotating motion creates a fan effect. The source created can be a jet (e.g. angle grinder with guard) or a doughnut-shaped cloud (e.g. disc sander).

Dust, Mist Enclose. Strip off the ‘boundary layer’ of dust-laden air moving with the rotating disc.

Fit a receiving hood to the guard.

Use LVHV (low volume high velocity extraction).

Other controls, e.g.: water suppression. Hot (and cold) processes Furnaces and casting. Soldering and brazing. Welding. Using liquid nitrogen

Hot sources – fume rises, expands, cools and mixes with the room air. Cold sources – the contaminant sinks.

Fume, vapour, gas. Enclose.

Receive the hot fume or cold contaminant cloud in a hood. Other controls, e.g.: control temperatures to reduce fume. Free-falling, solids, liquids and powders Falling liquid, powder or solid material. Conveyor transfer of powders/solids. Falling material induces a downward ow of air. If the material is a powder, there will be some shearing of ne particle-laden air at the edges of the stream.

The entrained air and dust may

Dust, vapour. Reduce the fall distance. Enclose. Seal gaps in conveyors. Partially enclose transfer points.

Process Examples Creation mechanism(s) and source description Form of contaminant Possible Controls Spraying and blasting Paint spraying.  Abrasive blasting Compressed air pressure

produces a jet that induces further air movement.

The contaminant cloud is cone-shaped.

 A paint spray gun can emit air at more than 100 m/s, extending more than 12 m.

Mist, vapour, dust. Reduce air

pressure, e.g. HVLP (high volume low pressure) spray gun.

Full, room or part enclosure.

Other controls, e.g. use water-borne abrasive; abrasive shot, hot mineral; electrostatic

methods for surface coating.  Abrasion Sanding. Grinding. Polishing. Fettling. Mechanical removal of surfaces create airborne dust

Dust. Capturing hood,

e.g. downdraught or back-draught table. Partial enclosure, e.g. booth.

LVHV systems. Other controls, e.g.: water suppression. Sweeping Dust and particulate

matter 

Re-suspending settled dust - a dust cloud moving in the direction of brushing.

Dust. Other controls,

particulate matter. e.g.: minimise dust leaks; vacuum system; wet cleaning.

Exhaust ventilation or extraction is the key to the majority of engineering controls for hazardous materials. The greater the extent of enclosure of the process, the more effective control is provided by the LEV.

Examples of partially enclosed systems include: ▪ Fume cupboards;

▪ Spray booths; and

Figure 2: Fume Cupboard

Where the process cannot be enclosed, ventilation can still be an important control measure. In particular, LEV ensures that the contaminant is reduced, as much as possible, at source, i.e. before it gets the opportunity to disperse into the wider environment where it may be inhaled by operators.

Figure 3: Welding Fume LEV

Examples of Local Exhaust Ventilation include:

▪ Flexible hoses and captor hoods which can be positioned to the source of the release, e.g. welding fume extractors;

▪ Extraction equipment associated with grinding wheels, etc. for these it is important that, as far as possible that the hood is in a position to collect the dust, within the direction of its movement;

▪ Lip extraction as used for solvent baths, etc; and

Figure 4: Typical LEV System

Hood

Ductwork

Filter Fan Discharge

The components of a LEV system include: ▪  An inlet (hood) to collect the contaminate;

▪ Ductwork to convey the contaminant away from the source;

▪ A lter (or other system) to remove the contaminant from the air in the duct;

▪  A fan or air moving device and ducting to the outside atmosphere (in some systems the cleaned air is recirculated to the workroom); and

Inlets

Inlets to LEV systems are of two major types:

a. Partial enclosures: Fume cupboards, spray booths, etc.

The source of the contamination is largely contained inside the enclosure. Air ows from the open face of the enclosure and across the source to extract openings in the booth, top, bottom or rear. Use can be made of physical properties associated with processes to bring about ventilation. For example, hot processes will result in contaminants rising with the heat and can be directed into a ue to exhaust to atmosphere.

b. Hoods: These vary in size and design depending on the application.

Hoods are of two basic types, receiving and capturing (sometimes referred to as receptor and captor).

 A Receiving Hood is one where the contaminate is forced towards it in some way, e.g. saw dust from circular saw is thrown in one direction, fumes from a hot tank rise.

 A Capturing Hood is required where the suction at the hood must be sufcient to draw the contaminant into it.

Figure 5: Partial Enclosure and Hoods

Receptor Captor

The inlet is the most important part of LEV system and requires careful design to be fully effective.

The important factor to consider with inlets is that their effectiveness reduces considerably with distance from the source of the contaminant. In fact the capture velocity at one duct diameter away from the face of the hood is about one tenth of the face velocity. Therefore, if the hood is wrongly positioned, this will result in virtually no capture of the contaminant.

For applications such as welding hoods, this fall-off in capture puts considerable importance on the operator to position the hood/partial enclosure correctly and move it as appropriate.

It is always important to ensure that the suction inlet is as close to the point of emission as possible in order to capture the contaminant effectively and as soon as it is generated, before it can enter the workplace atmosphere.

This difculty is addressed to some extent with some types of solder fume extractor which use ‘tool-tip’ extraction whereby a narrow extraction pipe is attached to the soldering iron tip and is moved with it by the operator.

Figure 6: Solder Fume Extractor 

The capture efciency (the amount of contaminant drawn into the LEV hood) is greatly increased by use of a ange. This is increased further the more enclosing the nature of the ange, as illustrated in Table 2.

Table 2: Effect of enclosure design on the airow required for Control  Airow required to give

effective control m3_s-1

Saving compared to plain extractor opening

Plain extract opening above bench

0.8 n/a

Flange added at rear of bench 0.62 22%

Enclosure extended at sides and above bench

0.59 26%

Transparent screen added at front of enclosure

It is important that the extraction inlet is designed to ensure an effective capture velocity (speed of airow in m/s at the inlet of the LEV). Different situations will require different velocities and therefore different solutions. Some examples are listed in Table 3

Table 3: Capture Velocities (Examples)

Source Conditions Typical Situations Capture Velocity (m/s)

Released into still air Degreasing tanks, Paint dipping, still air drying

0.25 - 0.5

Released at low velocity or into a slow moving air stream

Container lling, Spray booths, screening air-stream and sieving

0.5-1.0

Released at a moderate velocity or into turbulent air 

Paint spraying, welding 1.0-2.5 Released at high velocity or into

a very turbulent air-stream

Grinding, fettling abrasive blasting

2.5-10

The higher the required capture velocity, the greater the necessary air moving capabilities, ‘suction power’, of the LEV system as a whole. This has implications for the design of the ducting and motor as well as cost and energy efciency. Where a particularly high capture velocity is required, this is only really achievable with narrow ducting, resulting in a low volume of air. Otherwise the power required would be too great. Such systems are sometimes referred to as Low Volume-High Velocity (LVHV) systems.

Ductwork

Once the contaminant has been captured it needs to be transported via ductwork to the air cleaner. As with the captor design, the ductwork design should efciency. In particular, the following design factors need to be taken into account:

▪ Ducts should be of a suitable material not to be damaged by the contaminants (e.g. abrasive particles, corrosives, etc.);

▪ The system should be as simple as possible with a minimum number of bends, and as short as possible;

▪ Branches should join at the sides and be at an acute angle with respect to the air ow in the main duct;

▪ There should be an adequate number of inspection hatches and inspection points to allow proper cleaning and inspection. These should be at the top of the ducting;

▪ Flexible ducting (as opposed to rigid ducting) should be kept to a minimum since it tends to wear more quickly and offers higher resistance to air ow; and

▪ Noise through ducting can be a serious issue and care should be taken at the design stage to minimise this.

Figure 7: Good and Bad Ducting Design

Where there are several inlets to an LEV system, balancing will be required to ensure that there is a suitable air ow at each inlet. Without balancing, one inlet may have an excessive air ow at the expense of others which are then not adequate. This is often the case where an inlet is closer to the main branch and motor than outlying inlets, where longer pipe runs introduce losses and reduce the velocity of the air inlet. Balancing is achieved by opening and closing dampers in the ductwork placed at strategic places, normally before inlets and branches. Where an inlet is not in use, the damper may be closed to increase the capture velocity at other inlets.

It is also critical that the velocity of the air passing through the ductwork is sufcient to achieve the required transport velocity and to prevent settling of material. Recommended duct velocities depend on the contaminants being transported, typical minimum values are given in Table 4. Table 4: Recommended Minimum Duct Velocities (Examples)

Contaminant Duct Velocity (m/s)

Vapours, fumes, smoke 5-10

Light medium dust (e.g. sawdust) 15

 Average industrial dusts, e.g. silica, cement, grinding dusts

20 Heavy dusts, e.g. metal turnings,

wood chips

>25

Filters

For most extraction processes, a lter needs to be installed in order to protect the fan and to ensure that environmental contamination is minimised.

 A number of different design technologies for extraction equipment are available, it is important that the correct equipment is chosen for the application of concern.

Filters work in different ways. Some work by relying on the physical attributes of the contaminants – its weight, particle size or electrostatic properties, others on the basis of using wet or dry media e.g. scrubbers.

The following gure shows some of the typical types of equipment available: Figure 8: Types of Filters

In Line Air Filter Bag Filter

Cyclone dust separator Electrostatic precipitator

In Line Filters

These are simple ltration devices placed in duct work where particles are physically ltered out. High Efciency Particle Arrestor (HEPA) lters can be used to provide effective cleaning. Normally used for general ventilation systems. Good for ultra-clean environments and hazardous dusts (e.g. asbestos and biological agents)

Bag / Filters

These are suitable for dry dusts. Dusty air passes one way through a fabric layer that is exible and porous. The fabric may be constructed and treated to carry electrostatic forces which help attract and retain dust. Particles in the air are removed by:

▪ Impaction, where particles, larger than the weave, meet the surface of the lter; ▪ Impingement, where medium-size particles meet the bres within the lter weave; or  ▪ Diffusion, where small particles are attracted towards the bres.

The main ways to clean lters are: ▪ Mechanical shaking;

▪ Reverse airow; and ▪ Pulse-jet.

The cost of the lter material is a major expense. It is also an operating cost, as lters need periodic replacement before they fail. The designer should specify the replacement interval, which is normally between one and four years.

Cyclones

Cyclones consist of a circular chamber, tapered at the bottom. Dusty air feeds at a tangent into the top of the cyclone and swirls around the chamber. This throws particles out to the wall by centrifugal action. The particles’ velocities decrease and they fall to a collection hopper at the base of the cyclone. Cleaned air passes through a central outlet in the top of the cyclone. The larger the particle, the easier it is for a cyclone to remove it from the air.

Electrostatic Precipitator 

Dust particles are given a charge and attracted to plates of opposite charge they are then collected in a dust hopper. The arrangement consists of wires suspended in either vertical tubes or between charged plates. However, Some materials do not charge easily and will pass through the electrostatic precipitator 

Venturi Scrubber and Self Induced Spray Collector 

Dust-laden air passes through a venturi throat where water is injected. The highly turbulent conditions around the throat break down the water into small droplets which form around the dust particles. These are then separated in a cylindrical chamber (scrubber) where the water and sludge collect at the bottom and clean air passes through the top

Fans

The fan is the most common air mover. It draws air and contaminant from the hood, through ductwork to discharge. There are ve general categories of fan:

1. Propeller; 2. Axial; 3. Centrifugal;

4. Turbo exhauster; and

5. Compressed-air-driven air mover  Figure 9: Fans

Propeller Axial Centrifugal

Fan Selection

For a particular application, many factors need consideration for fan selection. These include: ▪ The type of substance in the contaminant cloud;

▪ Flammability or combustibility; ▪ The airow required;

▪ The system resistance characteristics; ▪ The fan pressure characteristics; ▪ Space limitations;

▪ The method of mounting the fan, and the type of drive; ▪ The operating temperature; and

Discharge to Atmosphere

The nal element of the LEV system is the discharge stack which takes the cleaned exhaust air from the fan and expels it into the atmosphere. Key issues to consider regarding the stack include:

▪ Positioning to avoid air re-entering the building;

▪ Positioning to ensure that discharge stacks are not discharging air which then enters air inlets;

▪ Ensuring that the stack is discharging at an appropriate height to ensure dispersal of the emissions. This depends on the material, but typically should be at least three metres above the building height; and

▪ Ensuring that the termination of the stack is appropriate to ensure efcient air-ow, prevent ingress of rain water and assist fume dispersal.

Emissions to Atmosphere After Installing LEV

Systems

The purpose of LEV systems is to extract a contaminant from the workplace, remove it from the air and discharge the cleaned air to atmosphere.

No cleaning system for the air is 100% effective, so there will always be a degree of residual contamination into the atmosphere.

 A major consideration is that many processes are subject to environmental regulation which may specify discharge limits for the contaminant. Regular monitoring and testing of the discharges to atmosphere may be required to ensure compliance with such discharge limits.

LEV systems are designed not only to comply with the health and safety requirements of protecting the workers but also with environmental considerations. Even with effective maintenance, problems can occur which may lead to a breach of local consent limits. For example, a bag in a bag lter can burst letting through a high quantity of contaminant.

Even when working within the consent limits for discharge to atmosphere, there may be circumstances where this will lead to a nuisance complaint. For example, in still air conditions when very small quantities of dust are discharged, the dust will tend to drop out of the atmosphere and complaints are likely if it lands onto parked cars.

 Assessing the Performance of LEV

Sometimes it is possible to judge the likely effectiveness of systems by simple observation. However, the judgement requires testing and the ndings need to be recorded. Observation includes judging the adequacy of make-up air. Inspection within ducts etc requires an endoscope, bre-optic camera or boroscope.

Qualitative Inspection

The use of smoke tubes and dust lamps can provide a qualitative assessment regarding the performance of an engineering control, e.g. LEV.

Smoke Tubes

The movement of air into hoods and inlets can be detected by injecting smoke into the moving airstream. By slowly moving the smoke tube away from the hood / inlet it is also possible to observe the range of inuence of the hood / inlet. It should be noted however that the smoke might not behave in the same way as dust particles.

Dust Lamp (Tyndall Beam)

 A shaft of light which illuminates a cloud of oating dust, is an example of light scattering by airborne particles. The phenomenon is often termed the ‘Tyndall effect’ , after the British scientist (John Tyndall, 1820-93) who rst investigated it.

Dust in the respirable range (less than 10 microns diameter) can be seen and photographed when illuminated by a high intensity beam of light. The dust cloud should be observed by looking up the beam towards the source of illumination against a dark background. In the absence of effective control measures, airborne particles are released into the workplace atmosphere by many industrial processes. Such particle clouds can be invisible under normal lighting conditions, but may be made visible by the use of the high intensity beam of light. This technique is commonly referred to as the dust lamp.

Use of the lamp enables the existence of particle release at a process to be simply demonst rated, or the performance of an extractor system to be assessed. Photography or video recording can be used to make permanent records of the observations. The dust lamp can be used in a variety of ways that include:

▪  As a tool to investigate work operations and processes to gain an understanding of the potential for exposure before any air sampling is done;

▪ After air sampling has demonstrated signicant over-exposure, as an aid to understanding how and why exposure is occurring; and

▪  As a useful tool in investigating the effectiveness of controls during their development in conrming effectiveness after installation and as, part of routine monitoring of controls.

Figure 11: Use of a Dust lamp

Quantitative Assessment Methods

Quantitative methods give a reproducible measurement of performance. Measurements alone do not provide direct evidence of control effectiveness, but the records are available for future comparison, as benchmarks. Methods include:

▪ Measuring the ow rates at various points including hood faces and ducts, hood ducts and the main duct;

▪ Measuring static pressures in various parts of the system including hood, ducting and the pressure drop across lters and fans; and

▪ The fan speed, motor speed and power consumption.

The types of tests and equipment include:

▪ Testing effectiveness with aerosol generation, and tracer gases with a suitable detector; ▪  Air velocity testing using an anemometer, eg thermistor or hot wire, velometer or a pitot

tube;

▪ Pressure testing with a manometer (eg inclined, anaeroid or micro);

▪ Filter or air cleaner performance testing: Equipment includes isokinetic and size-selective sampling, water quality test kit; and

Vane Anemometer 

Vane anemometers are suitable for measurements of face and capture velocities in metres per second for hoods, booths, enclosures and fume cupboards.

The measurements taken are compared against the design specication and previous readings to ensure the efciency of the LEV system is maintained.

Vane anemometers are similar to small windmills usually between 25 and 100 mm in diameter enclosed in a shroud with the rotating vanes mechanically or electrically coupled to an indicator. Figure 12: Vane Anemometer 

For large ventilation inlets the technique used, illustrated in Figure 13, is to divide the inlet into imaginary squares of approximately 150 mm and measure the face velocity at each intersection, ensuring the vanes are perpendicular to the inlet. An average is taken of the resultant readings, with each reading then compared to the average to ensure that there is not a wide range variation. Should a wide range be evident the airow distribution may require adjustment of bafes to achieve the design specication.

Hot Wire (Thermal) Anemometer 

The hot wire anemometer works on the principle that the rate of heat loss from a heated body is related to the ow of air passing over that body. The hot wire anemometer uses this relationship and the dependence of electrical resistance on temperature to produce an air velocity reading on a meter. This device can be used to measure velocities in the range 0-30 ms-1 and can also be used to measure air temperatures.

Hot wire anemometers are generally less suited to face velocity measurements, since they are difcult to direct precisely and they are also easily subject to damage or fouling. Their advantages however include a rapid response to changes in airow and a small head size, which can be inserted into small orices, for example to measure velocities in ductwork.

This device can also be used for the measurement of capture velocities at the actual point of release of the contaminant. This will indicate whether the positioning of the LEV hood is correct.

Manometers and Pressure Gauges

 A manometer is a device that measures pressure by the displacement of liquid in a U-tube or inclined gauge (low pressures). The manometer may be calibrated to measure the static pressure within a LEV system or to measure the pressure drop across a lter.

Pressure gauges measure the movement of a diaphragm or sprung coil and may be used as an alternative to manometers.

Pitot Static Tube

Duct velocities and static pressures are usually measured using a Pitot StaticTube. This instrument measures velocity pressure within a duct and consists essentially of two concentric tubes. The inner tube measures the total pressure in the system, and the outer one the static pressure.

The tubes are connected to either side of a manometer or pressure gauge. This instrument is best for air velocities above 3 m/s.

Static pressure measurements are taken behind each hood / enclosure and at various points in the ducting before and after the fan.

Figure 14: Pitot tube measurements of Duct pressure

Other Parameters

Other parameters used to measure the efciency of a LEV system include the fan speed, the motor current and, for systems that recirculate ltered air back into the workplace, the level of contaminant in the air.

Examination and Testing

Maintenance and thorough examination and testing need to be planned together in three stages : 1. Initial appraisal;

2. Regular maintenance including frequent visual inspection, maybe daily, weekly or monthly; and

3. Thorough examination and testing.

Initial Appraisal 

The initial appraisal has two major functions:

▪ To show that the plant works and meets its specied performance to control exposure; and ▪ To determine the operating criteria.

Regular Maintenance

Regular inspection and checking of LEV is not the same as the thorough examination and testing. The aim of the former is to identify potential problems so that they can be rectied before the LEV performance deteriorates. It is also necessary for maintenance purposes. The form that this inspection takes, and its frequency, will depend upon the nature of the plant. The regular inspection and checks may include:

▪ Ensuring that the LEV is always running when hazardous substances are being emitted or are likely to be emitted;

▪ Observing the condition of the suction inlet such as the hood, booth, etc to see whether it has moved or has been damaged;

▪ Observing the condition of any visible ductwork and dampers by the inlet;

▪ Observing any evidence of control failure, for example noticing if there are unusual dust deposits or a stronger odour than normal immediately outside the LEV;

▪ Observing any local instrument that has been tted to the LEV to show its performance, such as a pressure gauge on a lter or an airow device on a fume cupboard; and

▪ Undertaking any minor servicing such as emptying lter bins.

Thorough Examination and Testing 

Section 11 of the ILO Code ‘Safety in the Use of Chemicals at Work’ species that the exami nation and test for local exhaust ventilation (LEV) should provide correctly the information listed below: a. name and address of the employer responsible for the plant;

b. identication and location of the LEV plant, and the process and hazardous chemicals concerned;

c. date of last thorough examination and test;

d. conditions at time of test: normal production or special conditions (e.g. maximum use); e. information about the LEV plant which shows:

(i) its intended operating performance for controlling the hazardous chemicals; (ii) whether the plant still achieves the same performance;

(iii) if not, the repairs required to achieve that performance;

f. methods used to make judgements in respect of (e) (ii) and (e) (iii) above (e.g. visual, pres-sure meapres-surements, air ow meapres-surements, dust lamp, air sampling, lter integrity tests); g. date of examination and test:

h. name, designation and employer of the person carrying out the examination and test; i. signature or authentication of the person carrying out the examination and test;

 j. details of repairs to be carried out – to be completed by the employer responsible for the LEV plant.

Personal Protective Equipment

Respiratory Protective Equipment

(RPE)

Selection/Suitability of RPE

Respiratory protective equipment (RPE) can be split into two broad categories:

1. Respirators, which are designed to purify air by inhaling it through a lter medium which removes the contaminants; and

2. Breathing apparatus (BA), which supplies pure respirable air from an uncontaminated source.

Figure 15: Selection of RPE

The ambient air contains more than 20 % oxygen and there is no forseeable

immediate risk to life

The ambient air does not contain more than 20 % oxygen or 

an immediate risk to life could arise

 A ltering device may give adequate protection, as will appropriate breathing

apparatus

No ltering device gives adequate protection and appropriate breathing

apparatus should be used The choice of RPE will depend upon:

▪ The oxygen content in the atmosphere; and ▪ The toxicity of the hazardous substance.

Figure 16: Types of Respiratory Protective Equipment

Respiratory Protective Equipment (RPE)

Respirators

Filter out contamination in the air in thework place before it is inhaled by

the wearer 

Breathing Apparatus Provides uncontaminated air

from an independent source

Simple ltering respirators Power  assisted respirators Fresh air  hose BA Power  assisted airline Self  contained breathing apparatus (SCBA)

Respirators

This type of device relies on the wearer drawing air through a lter medium as they inhale. There are two main categories: Simple ltering respirators and power assisted respirators.

Simple Filtering Respirators

These range from disposable ltering facepieces, which are designed to be worn for no more than a shift and protect against particulate matter, to half and full face masks with detactable lters, which can protect against a range of vapours and particles.

 A full face mask is likely to provide a greater level of protection as well as including full face protection.

Figure 17: Filtering Respirators

Power Assisted Respirators

This type of respirator uses a motor to draw air through a lter (often located on the back of the operator). The air then blows through a face mask, creating a positive pressure and out.

Such masks have the advantage of increased comfort and generally provide greater protection by virtue of the positive pressure preventing inward leakage. Powered respirators can also be linked to hoods and blouses.

Figure 18: Power Assisted Respirator with Full Face Mask

Type of Filtering Medium

For a ltering respirator, selection of a ltering medium suitable for the type of contaminant is important. In particular, a mask suitable for dusts will not be suitable for gases vapours and solvents. A range of lter types is therefore available and is summarised in Table 5:

Table 5: Filter Types

Substance FilterType Colour  

Particulate

Organic gases and vapours (BP>65C)

 A Brown

Organic gases and vapours (BP<65C)

 AX Brown

Inorganic gases and vapours (excluding CO)

B Grey

Sulphur dioxide and other acid gases and vapours

C Yellow

 Ammonia and organic ammonia derivatives

K Green

Oxides of nitrogen NO

(must incorporate P3 lter – single use only)

Blue-white

Mercury Hg (must incorporate P3 lter

 – maximum use 50 hours)

Red-white Specic substances SX (and name of specic

chemical) if combined with P lter)

Breathing Apparatus

These rely on a supply of fresh air, either:

▪ From an air hose whose outlet is in an uncontaminated atmosphere and relies on the operator’s lung power to draw in the fresh air. In low risk situations a hose up to 36 m in length may be used to draw air at atmospheric pressure from outside a conned space. A bellows or fan may be used to assist in overcoming the resistance to breathing;

▪ From an air line using a compressor to provide a powered supply of ltered breathable air.  Air lines have the advantage of potentially unlimited length of use but potential concerns

regarding entanglements and obstructions; or 

▪ From self-contained breathing apparatus, which may be open or closed circuit.

Open Circuit 

These systems supply air to the wearer from a cylinder either worn on a back pack or from a remote location. A positive pressure system is often used, this ensures that any leakage (due to poor face seal for example) will be outwards. The back packs are heavy and restrict movement but avoid the problem of entangled hoses. A single cylinder allows around

40 minutes of use.

Closed Circuit 

These systems remove excess carbon dioxide from exhaled air which is then re-breathed by the wearer. This type of apparatus is generally only used for emergency self-rescue purposes. Figure 19: Self Contained Breathing Apparatus

 Assigned Protection Factor 

Some designs of respirator are inherently more effective than others. It is important that the level of protection chosen is appropriate to the application.

The minimum protection required from the RPE is determined using the equation:

Workplace concentration outside the facepiece of the RPE

Minimum Protection Required

(MPR) =

Maximum allowable concentration inside the facepiece of the RPE

The maximum allowable concentration inside the face-piece is determined by consulting national or international standards and taking account of ‘in-house’ limits.

The MPR value is compared with the assigned protection factors (APF) indicated in Table 6, to identify suitable equipment.

The APF is the level of respiratory protection that can realistically be expected to be achieved in the workplace by 95 % of adequately trained and supervised wearers using a properly functioning and correctly tted respiratory protective device.

The APFs are guidance and protection levels below APF are possible when RPE is unsuitable for the task and is not suited to the wearer and the environment.

Where advice given in this guidance is properly taken into account, the wearer can achieve protection at or above the APF values indicated in Table 6. APF values higher than those shown in Table 6 need to be based on objective workplace performance data that will stand up to scrutiny.

Table 6: Typical NPF values for Respiratory Protective Equipment

Abreviation Meaning Protection Factor  

P1 Efciency of particle lter  4

P2 10 P3 40 FFP1 Halfmask 4 FFP2 10 FFP3 20 FMP1 FaceMask 4 FMP2 10 FMP3 20

TM1 Powered (fan assisted) resp with mask 10

TM2 20

TM3 40

TH1 Powered (fan assisted) resp with hoods 10

TH2 20

TH3 40

LDM1 Constant ow airline BA with mask 20

LDM2 20

LDM3 20

LDH1 Constant ow airline BA with hood 10

LDH2 20

LDH3 40

Constant ow airline BA full face mask 100

Constant ow airline BA suit 200

SCBA Positive demand full face mask 2000

The ‘real life’ performance of respiratory protection will of course depend on how well the mask is tted. For particularly hazardous environments, such as work with asbestos, it is strongly recommended that masks be ‘t tested’ to user’s faces, using a Quantitative Fit Testing Device, based on a particle counter.

Table 7: Factors to be Considered When Using RPE

Factor Effects Comments & Recommendations

Length of time RPE is worn

Face masks become uncomfortable when worn properly for long periods (e.g. > 1 hour)

Wearers may be tempted to loosen or remove RPE

Blowing the nose or scratching is not possible less tiring to wear for long periods

Respiratory stress decreases capacity to work

Provide a choice of RPE to allow wearers to select the most comfortable

Loose-tting facepieces may be preferred, if suitable

Powered / assisted RPE is generally

 Arrange frequent work breaks in a clean area to allow removal of RPE Physical work

rate

High breathing rates cause high peak

inhalation ows, and amplify breathing

resistances of equipment

Some RPE is heavy to carry and can cause physical strain

Overall work capacity will reduce

Excessive sweating can cause facepieces to slip and leak

Powered / assisted RPE is less tiring to wear than simple respirators

Compressed-air supply should be able to provide at least the peak inhalation ow needed

Modify the task to reduce heat stress

 Arrange adequate rest breaks Provide active cooling

The physical size and weight of RPE can restrict movement where there is limited space

Trailing airlines can drag, snag or be a tripping hazard

Eliminate restricted space / modify access ways to allow free use of RPE

Train users in negotiating tight spaces

Select less restrictive RPE – ltering devices or SCBA where suitable,rather than types with a trailing tube / hose

Keep tube runs as short as possible or manage effectively

BA which allows temporary

breathing through a suitable lter on disconnection from the supply line allows safe exit from the hazardous area, or movement to another  supply point so that work can resume

Factor Effects Comments & Recommendations Visibility Reduced peripheral vision and ability

to see ne detail

Misting, scratching, abrasion or contamination of the visor due to use

Use the least restrictive design of facepiece

Provide adequate lighting in the work area

Powered / air supplied RPE is more resistant to internal misting

Provide and use cleaning

materials as recommended by the manufacturer 

Some visors may be treated / coated to reduce misting Some facepieces may have

additional ‘tear-off’ visors to protect the main one

Other PPE Incompatible with other PPE,

making either or both ineffective and uncomfortable

Cumulative effects, e.g. combined weight and heat stress of having to wear RPE and heat / ame protective clothing

Where possible use integrated protection, e.g. a powered helmet respirator rather than separate head, eye and respiratory protection, or an air-fed full suit rather than impervious unventilated clothing and separate RPE

Where no integrated RPE exists, consult manufacturers for information on compatible equipment

Communication All RPE inhibits normal

communication (speaking - and hearing) to some degree, causing difculty in being understood

Devices which hide the mouth hide ‘lip reading’ clues to speech, though hoods and visors may not

Many full face masks incorporate a ‘speech diaphragm’ to make talking more easily understood

Hoods / helmets can make hearing difcult – NB warning systems Communications systems are available, e.g. radio linked, or incorporated into the air supply line

Factor Effects Comments & Recommendations Work

environment

Chemical hazards - solids, liquids, gases and vapours

Physical hazards - heat, ame, radiation, impacts and sharp edges

Biological hazards - contamination and infection of equipment and wearer 

RPE should be resistant to any chemical, physical or biological hazards identied in risk

assessment

Manufacturers will be able to advise on compatibility

Optional accessories may be required, e.g. impact-resistant or resistant visor, chemical-resistant or general purpose supply tube, splash guards

Intrinsically safe, light, alloy-free, anti-static equipment will be required in explosive atmospheres Training To be effective RPE, as with all

other types of PPE must be properly selected and maintained

Complex types of RPE will require a level of competence before staff are able to use it safely and effectively Staff may need to be trained to t, adjust, inspect and maintain RPE

Storage of RPE

Safe and clean storage facilities for all RPE must be provided.

There should be procedures for people wearing RPE to have comfort, tea, meal and other breaks in safety.

Maintenance of RPE

 All RPE should be checked for correct functioning before each use in line with the manufacturer’s instructions.

Maintenance is a requirement for all RPE, except for single use RPE, and should be carried out by properly trained personnel.

Thorough maintenance, examination and tests should be carried out at least once a month. However, if the RPE is used only occasionally, an examination and test should be made before use, and in any event the interval should not exceed three months.

Emergency escape-type RPE should be examined and tested in accordance with the manufacturer’s instructions.

Only spare parts from the original manufacturer should be used during maintenance and repair of damaged RPE.

Face Fit Testing

Fitting the Mask 

Respirators are available in different designs and sizes. Some are valved and some unvalved  – both options provide a high level of protection when worn correctly.

Fit testing is a means of assessing how well a respirator seals to a face:

▪ It has to be an individual test because one model will never t all and every face is different; ▪ Fit tests may fail, and protection will be lost, if the mask isn’t being worn properly; and ▪ Sometimes a mask simply won’t t an individual, but often a better t can be achieved by

taking more care when putting it on. Wearers must be clean-shaven to get a good t with a respirator.

Qualitative Fit Testing 

To ensure that the mask is effective face t testing is always recommended this involves a range of potential test methods depending upon the mask being tested.

Sensitivity Test

This method uses a sensitivity measure using bitrex or saccharin. The test is done without wearing the respirator to check if the user can taste the test solution. This qualitative t testing is a simple pass/fail test based on the wearer’s subjective assessment of the leakage, via the face seal region, of a test agent. These tests are relatively simple to perform and are suitable for half masks and ltering facepieces. They are not suitable for full-face masks

Quantitative Fit Testing 

The facepiece should be equipped with a sample probe positioned within the breathing zone of the wearer and at a position near to the wearer’s lips. The open end of the sampling tube should be positioned close to the wearer’s face (<10mm) and approximately mid way between the nose and mouth. Taking an air sample from inside the facepiece that is representative of the in-facepiece concentration may be improved with the use of a suitable multiple-hole sampling probe. There are two main test methods:

▪ Laboratory Test Chamber Method .

The test can be carried out in a chamber into which a standard challenge of either sodium chloride (NaCl) aerosol, or sulphur hexauoride (SF6) gas can be delivered. The leakage of the test challenge into the f acepiece under test is measured while the wearer walks on a treadmill and performs a series of exercises. The extent of the test agent leakage is expressed as percentage inward leakage and then converted to t factors.

▪ The Controlled Negative Pressure (CNP) Fit Test Method

This is based on exhausting air from a facepiece correctly  tted on the wearer’s face to generate and then maintain a constant negative pressure inside the facepiece. The rate of air exhaust is controlled so that a constant negative pressure is maintained in the respirator during the t test.

Both these methods can be used for ▪ Filtering facepieces P2, P3 types; ▪ Half mask respirators;

▪ Full face mask respirators;

▪ Power assisted respirators with full face mask or half mask; and

▪ Breathing apparatus (including air supplied, self-contained and escape types) with fullface mask or half mask

Figure 20: Fit Test methods

Sensitivity Test:

Laboratory Test Chamber Method

Skin Protection

The main skin protection relates to the hands and arms.

Gloves

Effective hand protection can only be achieved if the type of glove selected is suited to the wearer, the exposure risk and the work task.

Gloves, as with all PPE should only be used where risk assessments show that they are the best control option when other methods are not reasonably practicable or as a supplement to other control measures.

 Although some types of glove offer very high levels of protection, no protective glove can provide 100% protection against exposure to hazardous substances. Many studies have shown that levels of protection in the workplace are much lower than in tests under laboratory conditions.  As a general rule, glove protection levels can be reduced by up to 75% when the gloves are in

active use.

This is not because there is any deciency in the standard of protective glove manufacture but because there are many complex issues surrounding the use of protective gloves in the workplace.

The limitations of gloves as a control measure can be summarised as:

▪ Gloves only protect the wearer - they do not remove the contaminant from the work place environment;

▪ Gloves may be inconvenient and interfere with the way people work (e.g. be uncomfortable, restrict movement, or affect sense of touch);

▪ Gloves may introduce new hazards, e.g. latex and corn starch allergies;

▪ Gloves will not afford adequate levels of protection unless they are properly used and maintained (they may be affected by physical and chemical damage, ageing, exing and stretching and poor maintenance); and

▪ Physical and environmental restrictions imposed on protective glove wearers may adversely affect work rates.

Chemical protective gloves are available in a wide range of natural and synthetic materials, but there is no single protective glove material (or combination of materials) which gives unlimited resistance to any individual or combination of chemical agents.

There are three ways that protective gloves will, at some stage, fail to protect the wearer from exposure to chemical agents. These are:

1. Degradation: A deleterious change in one or more properties of a protective glove material due to contact with a chemical.

These changes include aking, swelling, disintegration, embrittlement, discolouration, dimensions, appearance, hardening, softening, etc.

2. Penetration:  The movement of a chemical and / or micro-organism through porous materials, seams, pinholes, or other imperfections in a protective glove material on a non-molecular level.

3. Permeation: The process by which a chemical moves through a protective glove material on a molecular level. Permeation involves the following:

▪  Absorption of molecules of the chemical into the contacted (outside) surface of a material;

▪ Diffusion of the absorbed molecules in the material; and

▪ Desorption of the molecules from the opposite (inside) surface of the material. Gloves can be classied with a permeation performance levels based on ‘breakthrough times’ (the elapsed time between applying the test chemical to the external surface of the glove and its subsequent presence on the internal surface).

Table 8: Permeation Performance Levels

Measured Breakthrough Time (mins) Permeation Performance Level

>10 1 >30 2 >60 3 >120 4 >240 5 >480 6

Table 9 gives a brief example showing breakthrough times for common materials with specied chemicals.

Table 9: Breakthrough Times for Common Materials with Specied Chemicals

Acetone HCL NaOH Toluene Xylene

Rubber  7 mins 211 mins >8 hr Not Tested Not Tested Neoprene 12 mins >8 hr >8 hr 21 mins 30 mins

Nitrile NR NR NR 20 mins 65 mins

PVC NR 5 hr Not Tested NR NR

Butyl >8 hr >8 hr >8 hr 20 mins 65 mins NR = Not Recommended

Other factors to be considered when selecting gloves include the requirement for wrist and forearm protection and the likelihood and degree of mechanical damage.

Problems have resulted, for example where ‘dipped’ plastic gloves have been used for applications involving signicant quantities of oil or solvent. These general purpose gloves are manufactured by dipping a typical cotton glove in a polymer material which coats most of the glove, but leaves the cuff uncovered. There is a risk in some situations where the cuff can become soaked in oil and cause skin problems to the wrist of the wearer.

There is also a risk of dermatitis from prolonged wearing of gloves due to the skin of the hand being unable to ‘breathe’ and sweat re-absorption. Such risks need to be balanced.

Skin Creams

These can help to protect the hand. So called ‘barrier cream’ can provide some protection against chemicals and may in particular make hands easier to wash dirt and grease from, which will save the skin from some aggressive scrubbing.

However, claims that barrier creams can offer a high level of protection against chemicals and be an ‘invisible glove’ should be viewed with scepticism. In general, barrier creams are not considered to be a preferred option as the degree of protection is very variable.

 After work creams can help to put back natural oils into the skin, which may have been removed by contact with chemicals or intensive washing. It must be borne in mind, however that some workers may be allergic to such products.

Eye Protection

There are three main groups of occupational hazards: ▪ Mechanical;

▪ Chemical and biological; and ▪ Radiation.

This element is concerned with chemical and biological hazards, however circumstances may arise where mechanical or radiation hazards are also present. Therefore eye protection may well need to afford protection against a range of hazards.

Table 10: Examples of Chemical Hazards to the Eye, with Occupational Sources

Example Hazards Example Sources

Chemical splashes Bleaching, battery lling, electrolytic plating, degreasing, paint stripping, chlorination processing, cement mixing Liquid aerosols Crop spraying, paint / lacquer spraying, fumigating Steam jets Leaking pipe-work, pressure vessel venting

Fine dusts and powders Cement mixing, wall sanding, lime spreading, powder coating

Fumes, vapours and gases Varnishing, adhesive bonding, exhaust gas analysis, welding, soldering, fumigation

Biological agents Veterinary work, dental surgery, rst-aid, medical research, waste management

Table 11: Features of Eye Protection

Style Key Features

Spectacles

May be twin type ocular (conventional

spectacle frame) or single ocular (eyeshield)

Twin type oculars may incorporate prescription lenses. Eyeshields may be worn over corrective spectacles Both types protect the eyes but offer limited

protection to the orbital cavities

Side shields or deep side arms afford limited lateral protection to the orbital cavities

Goggles

May be box type (single oculars) or cup type (twin oculars). Both types are held in place with a headband and protect both the eyes and orbital cavities

Box type may be worn over corrective spectacles, cup type can not

Ventilation may be incorporated to address problems of misting

Face shields

Comprises a moulded visor attached to a brow shield and headband

Provides protection to all, or part of the face, as well as the eyes

May be integrated with safety helmets May be worn over corrective spectacles

Training

▪ Employees should be made aware of why it is needed, when it is to be used, repaired or replaced and its limitations.

▪ Employees should be trained and instructed in how to use it properly.

▪ Because PPE is the last resort after other methods of protection have been considered, it is important that users wear it all the time they are exposed to the risk.

▪ Employers should check regularly that PPE is being used and investigate fully any reasons why it is not. Safety signs can be useful reminders to wear PPE.

Maintenance

The employer should make sure equipment is:

▪ Well looked after and properly stored when it is not being used, for example in a dry, clean cupboard, or in the case of smaller items, such as eye protection, in a box or case; and ▪ Kept clean and in good repair follow the manufacturer’s maintenance schedule (including

recommended replacement periods and shelf lives). Simple maintenance can be carried out by the trained wearer, but more intricate repairs should only be done by specialists.

Conclusions

The control of hazardous substances is in accordance with basic hierarchical principles. Prevention is better than protection, and safe place strategies take priority over safe person strategies.

Elimination of the hazardous substance is the best option, followed by the substitution of materials or work processes.

Local Exhaust Ventilation is often a key component of systems for the control of airborne contaminants. To be effective it must be properly designed, installed and maintained.

Personal protective equipment is the weakest option as:

▪ It does nothing to prevent or reduce the hazard itself but looks to protect the wearer from the consequences of the harmful event;

▪ It is heavily dependent upon management controls for the selection and maintenance of appropriate equipment and the training and supervision of the wearers;

▪ It relies heavily on the competence and goodwill of the wearer and thus its effectiveness can be affected by the range of human factors; and

▪ If it fails it can only fail to danger and the wearer will be harmed.

Ultimately the level of risk will determine the nature of the precautions to be taken. Often a combination of control measures is required