Last reviewed 15 April 2014
Fire-fighting foam is not just used at major petrochemical fires, such as at Buncefield. It can be used at any smaller locations where hydrocarbons are being stored or used. Alan Field explains what to be aware of should a fire take place and the subsequent pollution risks.
Water is the fire-fighting substance (or fire suppression medium) we think of first. Yet for some fires it is entirely unsuitable and can make matters worse; for example, any fire involving flammable liquids (including petroleum based products and solvents) — sometimes referred to by fire engineers as Class B materials — might need to be extinguished by foam.
Foam is simply a substance that creates a stable blanket, or layer, of bubbles across the fire to starve it of oxygen. There are many different types of foam for specific applications. Some foam concentrates are also designed to cool down the fire or suppress flammable vapours escaping from the fire.
There are also some experimental systems using compressed air, water and foam (sometimes known as CAFS) to deploy on a much wider range of fires but these are outside the scope of this article. The same applies to high expansion foam (sometimes referred to as Hi-Ex). This is typically deployed in basements, tunnels or hangers to deluge the entire void space where the fire is located.
This article will focus on the more typical small to medium-sized enterprise (SME) scenarios where conventional low to medium expansion foam is deployed on fires involving Class B substances in tanks, others storage areas (such as a warehouse) or in a production area, such as paint shop.
What is foam?
Foam is created by a mixture of foam concentrate, water and air. One way of creating it is by using a specialist nozzle or “branch” on an extinguisher, attached to a fire hose, or on a fixed monitor. The other way is by mixing the concentrate, water and air through a device called a foam proportioner, normally aligned to a fire pump, either in a building or on a fire engine. The expansion rate of foam changes its characteristics and applications. It will be necessary to determine whether low or medium expansion foam is better for the particular risk involved, this should be decided as part of a risk assessment and/or as control measures are developed.
Foam can be delivered by extinguishers of varying sizes, eg fixed fire-fighting installations in the building or around the storage tank, or by the fire service bringing their own foam tenders (a fire engine that carries foam concentrate in bulk) to the scene of the fire.
Some important points
There are a number of factors to be aware of if an SME uses or stores Class B materials.
A fire risk assessment needs to consider the kinds of fire suppression media that might need to be used on site. Suppression media other than foam might be recommended, especially if the quantities of Class B materials are relatively small. These might include carbon dioxide or dry powder (sometimes known as ABC powder), depending on the circumstances.
Where the business has insurance surveys conducted, then the underwriters may have specific requirements or advice in terms of fire suppression equipment. Also, if specialist fire protection engineers are consulted they may have specific recommendations or approaches.
Sometimes fixed fire suppression installations will be recommended, either because of the quantities of flammable liquids stored or for other reasons such as the fact there is a significant risk of fire after normal working hours. These will typically be operated after a smoke or heat detector actuates them. It may be a foam deluge system or, sometimes, be combined with different systems using other media. There are many different systems but all require regular maintenance and inspection. Management should be fully aware of why such a system has been recommended, how it operates and, most importantly, how it fits in with the overall fire protection of the site.
If a management decision has been taken that staff should attempt to tackle small fires before evacuating the premises, appropriate staff need to be aware of the fire suppression media that will be deployed for different types of fire. This is something that needs to be decided as part of the overall life safety risk assessment and plan for the site.
Where different sizes of fire extinguishers may be used (eg some large foam extinguishers will be attached to a purpose built trolley) then designated staff need to understand how to operate every type, with hands-on demonstrations where necessary. In other words, the outbreak of fire is not the time to try and fathom out how a fire extinguisher works.
With most Class B fires, the fire service will deploy foam. Accept any opportunity to discuss with the fire service how they would respond to fire at the site. This is especially true where the quantities of flammable liquids are small and more conventional fire situations may arise. Equally, there may be other complexities on site — for example, the storage of acetylene gas for welding or, say, a warehouse with large numbers of aerosols. These would require their own specific emergency response in the event of fire and may impact on other scenarios involving Class B materials.
Pollution risks need to be considered in a risk assessment but this is sometimes overlooked.
There are always pollution considerations where foam might be deployed. Different types of concentrate may be more polluting than others, depending on the chemical constituents of the foam and other factors. This especially needs to be considered if environmentally sensitive areas could be affected by firewater or foam run-off.
The foam run-off (mixed with water and the burnt materials) can be toxic and certainly polluting, whether they go into watercourses or mains drainage. There will need to be a safe clean up on site of the run-off — even if the fire is relatively small — due to the amount of foam needed to extinguish a fire. These are all points that a risk assessment should take into account.
Under the Water Resources Act 2001 it is an offence to pollute a watercourse and, similarly, under the Water Industry Act 2001 polluting a sewer by discharging material without the prior consent of the water undertaking is also an offence. Therefore, risk assessments should always look at how foam run-off could, ideally, be isolated on site. Each site — and each budget — will present a number of different options.
For example, this might involve drainage interceptors, the bunding of tanks and the creation of “sacrificial areas” which are parts of the site designed to hold the run-off until it can be disposed of (normally by pumping into specialist road tankers). When the site could impact on an environmentally protected area, eg a watercourse with rare wildlife, particularly consideration must be given to ensuring run-off would not enter those sites.
Whichever options are chosen, it will be necessary to consider the capacity of these measures to hold the volume of run-off anticipated. The fire service or fire protection engineers can be asked to give an estimation based on the various possible scenarios.
The key point is that, in nearly all circumstances, the contaminated foam waste is the responsibility of the property owner, not the fire service.