Introduction:
Chemical firefighting itself is a vast subject as chemicals vary in their properties such as flammability, reactivity, toxicity and complexity increases due to combustion products. You cannot have universal solution for all the chemicals. Pyrophoric chemicals are different than other chemicals. The property of spontaneous ignition makes them special. The properties such as corrosive, water reactive, and peroxide forming pose a challenge for firefighters.
What are Pyrophoric Chemicals?
Pyrophoric chemicals can be in liquid, solid or gas phase, which has the potential to spontaneously ignite in air at temperatures of 54oC or below. They often also have corrosive, water reactive, and peroxide forming properties. Improper use of these materials has resulted in r fires, damage to property, injury and even death. The increased level of risk these properties present, calls for additional fire and safety standards to ensure safe handling of these materials.
Fire protection considerations:
Storage of Pyrophoric materials in Large storage tanks:
While storing and handling pyrophoric chemicals passive and active fire protections aspects are considered to limit the damage in case eventuality of fire.
Some of the passive fire protection considerations are as follows:
- Sloped floor
- Drain and safe burning area provided
- Distance between two tanks
- Separating wall height
- Optimum quantity of liquid per tank
- Maximum burning time
- Maximum pool area
- Maximum flame height
- Distance of tank from flame top
- Maximum heat load on nearest tank
Active fire protection has very limited scope for pyrophoric chemicals:
Water/fog is recommended for adjacent tanks but not on the tank in question. It may aggravate the problem but does not pose hazard of escalating fire to other containers.
Fixed DCP system is also recommended as it will douse the fire quickly. Further it may be controlled burning at burning pit.
Small fires (Lab scale chemicals):
Fire Extinguishers
- Class A, B, C (dry chemical), vermiculite and dry sand : For Metal Alkyl, pyrophoric liquids and supporting flammable solvents.
- Class D (recommended for certain materials) -For reactive metals
Do NOT use Extinguishers containing or developing water, carbon dioxide or halons. They are not suitable for firefighting as they react violently.
While fighting pyrophoric fire firefighter must use BA sets and appropriate chemical suit preferably D type.
Conclusion:
The approach to be taken to tackle the fire involving pyrophoric materials is very crucial. The best policy is to avoid loss of containment. In case of loss of containment feasibility of safe burning must be explored as a first preference of tackling the fire. It takes lot of practice and knowledge to control the fire. It is advisable to entrust the job with experienced fire fighters when it comes to use of water on pyrophoric substance. The water quantity should be large to suppress and negate the effect of violent reaction.
Ref: Pyrophoric Chemical Guide:University of Minnesota
CCPS
NFPA 750
AkzoNobel Technical bulletin