Only competent people should interpret guidance on application rates; in addition, they should be fully aware of their application, and have knowledge of actual fire incidents and resource deployment options.
(i) Tank fires
For major tank fires involving petroleum products, there are three main options:
— Controlled burn.
— System application of foam.
— Monitor application of foam.
All three strategies have been used successfully at different locations around the world. The final decision on the most appropriate strategy will depend on site-specific issues including the perceived risk, availability of water supplies and availability of trained responders. Clearly the site strategy should be reviewed and accepted by the local regulatory authority and appropriate incident preplans for both duty holders and responders should be developed.
One major problem at tank fires in the past has been
the unnecessary over-application of water to exposed tanks and to tanks on fire. The experience-based consensus is that provided the tank on fire is designed to API Std. 650 or equivalent (e.g. BS EN 14015), it should not be cooled except, perhaps, to help foam seal against the hot tank shell in the final stages of a fire. The tank shell above the contents will gradually curve inwards in a fire and not jeopardise the tank shell integrity. Some cooling may be required eventually to assist any foam seal against the tank wall.
The maximum recommended thermal radiation exposure level for unprotected tanks (i.e. having no active fire protection or PFP) should be 8 k W/m2 or 32 kW/m2 for protected tanks (see section 2.6.2). This, with the availability of validated radiant flux calculation programs, allows a more rigorous analysis of fire-fighting water requirements.
Incident experience has demonstrated that monitor application of foam can be a successful way of extinguishing large tank fires providing the response is well planned, the required resources are available and foam logistics (see section D.11(iv)) are carefully considered. In practice, actual application rates for the largest successfully extinguished tank fires have been in excess of the minimum application rates specified in publications. Consequently the minimum application rate should be 10,4 l/min./m2 (see section D.9(v)); however, this may need to be increased to achieve extinguishment.
Regarding incident duration, petroleum and its products on fire in a tank, will typically burn down at a rate of approximately 2-4 mm/min. Incident duration has been reduced in some cases by pumping out the fuel from the base of the tank into spare tanks a safe distance away.
Note however, the proviso regarding boilover in section D.11(ii)).
(ii) Boilover
The phenomenon of boilover in crude oil storage tanks remains of major interest and opinions are divided over the effects of fire-fighting strategies on its probability and consequences.
The boilover mechanism is described more fully in section 2.5.5.7. Essentially, the height of the boilover and the lateral spread depends on the characteristics of the crude, the amounts of water crude in the tank as well as ambient conditions. Some boilover events will be more severe than others. However, from a fire-fighting perspective it should be assumed that once a crude tank full surface fire develops, a boilover will always occur unless the fire is extinguished.
What is less clear is the effect of application of large amounts of water and/or foam to the tank and whether this
can actually speed up the boilover mechanism or result in more severe consequences. The effect of fire-fighting media application on boilover probability and consequences is not fully understood, although work is being carried out internationally to establish this.
In addition, work is being carried out internationally to establish the exact mechanisms present for boilover to occur, and whether indeed boilover is inevitable. Also, opinions are divided as to whether boilover can occur in certain other denser products such as fuel oil.
Regarding fire-fighting strategies, it should be noted that pumping out of product is one option that could reduce the consequences of a boilover (since less product would be present to boil over) but it is generally accepted that doing so would probably reduce the time taken for boilover to actually occur. It has also been suggested that hot zone formation (if this is indeed the dominant boilover mechanism) could be tracked using available equipment such as thermographic cameras, thermocouples etc. to predict time to boilover. However, work is still continuing to establish practical fire ground techniques useful in predicting boilover time and consequences.
(iii) Bund fires and process area fires
Bund and process area fires have been successfully extinguished using both fixed systems and mobile means.
With regard to foam application, standards such as NFPA 11 recognise that portable monitors, foam hose streams or both have been adequate in fighting spillage fires. There is also a suggestion that in order to obtain maximum flexibility due to the uncertainty of location and the extent of a possible spillage in process areas and tank farms, portable or trailer mounted monitors are more practical than fixed foam systems in covering the area involved. However, there are logistical issues to address and in some cases a fixed or semi-fixed system may be appropriate depending on staffing, training and availability, etc.
It should also be recognised that large throughput monitors may not be the most appropriate choice for fighting process area fires. In particular, large volumes of water or foam delivered at high pressure might make an incident worse by rupturing pipework, damaging equipment or causing product 'carry over'. In many cases, mobile foam trolleys or wheeled extinguishers may be the most suitable equipment for fighting relatively small spillage fires.
As always, incidents should be reviewed by risk assessment, as part of an FEHM approach, and equipment should be matched to the scenario for suitability, application rate and system run-time.
(iv) Foam logistics
Bulk movement and supply of foam concentrate represents a major logistical problem which, if not carefully considered, planned and rehearsed, may delay foaming operations and, in some instances, will prevent effective and continuous foam application. It should be remembered that once foam application commences onto a fire, it must be maintained uninterrupted for the duration required.
The use of 25 l foam concentrate drums is not a viable option for supply of foam concentrate during a large storage tank fire. The capacities of foam monitors for large tank fires would typically begin at 4 500 l/min., which at 3% proportioning rate would require 135 l/min.
or more than five drums each minute.
Although many occupational fire brigades favour 200 l drums for supply, these will clearly last for less than 1,5 minutes assuming a 4 500 l/min. monitor is in use.
With monitor flowrates above 4 500 l/min., the 200 l drums are consumed rapidly. These drums are therefore of no benefit if large throughput foam monitors of 30 000-60 000 l/min. are to be used.
One option may be to use large capacity IBCs of 1 000 litres or more, which can be transported using flatbed trucks or fork-lift vehicles to each fire vehicle (or monitor) and delivered to the spot within foam suction hose reach. Having two or more within suction hose reach will clearly increase the duration before changeover and therefore give more time for transport crews to keep re-supply moving. If the containers have a side-top mounted funnel point the containers can be stacked at the vehicles or monitors.
Using foam tankers in the range of 10 000-15 000 l capacity is the other method of supply, but this needs large assets/procurement in the form of foam tankers dedicated only to a full surface large tank fire and these would have to be onsite within a very short period of the incident start.
(v) Environmental issues
The environmental protection consequences of a controlled burn policy for tank fires are, essentially, smoke production. Some limited data on the toxic effects of smoke from petroleum products are available. It is recognised that the environmental effects of controlled
burn may be preferable to the potential effects of over-application of water and/or foam and the potential for run-off to run-offsite areas caused by this in some circumstances.
Another environmental issue for tank fire-fighting is that of fluorosurfactants in foam. At the time of writing all proven foam concentrates that are effective contain fluorosurfactants. There is continuing work in this area but no firm conclusions regarding acceptable policies have been developed at the time of writing of this publication.
For process area fires, the consequences of controlled burn may be more severe, depending on escalation potential. There will, in many cases, be a requirement to fight the fire, and fire-fighting water runoff and limiting its consequences will be a major consideration.
(vi) Fire and rescue services response issues
FRSs have water tenders as the main response units to incidents. There may be special foam carrying or other vehicles where the need has been identified. These may include emergency tenders for rescue or large scale BA incidents, foam tenders (which are not recognised as petroleum industry foam tenders but will carry limited quantities of foam concentrate, hydraulic platforms or aerial ladders, command and control vehicles, etc.).
Water tenders will typically feature a water tank of 2 250 l and a fire-fighting water pump in the order of 2 250 l/min. There may be some units that can pump 4 500 l/min., depending on the brigade, its area of response and the facilities within.
The type and number of foam monitors carried by FRSs is very limited. Water tenders will typically carry one or two foam branches of 225 l/min. or 450 l/min.
capacity, together with an inductor. Some brigades may have one or two larger capacity foam monitors but will not usually hold the numbers and capacity of foam monitors necessary for larger incidents such as tank fires.
Taking these factors into account, it is considered that the unofficial role of FRSs during major fire incidents is to respond and provide trained and disciplined personnel for hose deployment, water and foam monitor deployment and foam supply.
There is therefore a clear need to ensure that a competent industry response team will mobilise the major resources required and provide the guidance and expertise to FRSs to deal with the incident, if necessary.
ANNEX E
EMERGENCY RESPONSE TEAM MEMBER – EXAMPLE COMPETENCY PROFILE
E.1 INTRODUCTION
This annex provides an example ERT member competency profile based on four units: operations;
maintenance; procedures; and skills.
E.2 COMPETENCY MAPPING PROFILE