BY KEVIN L. KREITMAN
A local fire department arrives on the scene of a working fire. The incident commander (IC) sizes up the situation and, intending to extinguish the fire, instructs fire crews to begin pumping on the fire 92 pounds of hydrogen and 742 pounds of oxygen per minute.
Sound farfetched? Think again; it happens all too often in the United States. ICs and firefighters have been giving and receiving the erroneous information that a combustible metal fire can be extinguished if enough water is applied. This is an extremely dangerous idea and puts responders and communities at needless risk.
Combustible metals such as magnesium, titanium, zirconium, tantalum, lithium, and sodium are becoming more prevalent in use, shipment, and recycling. Significant quantities of these metals may exist in or travel through your jurisdiction, and you don’t even know it. Vehicle manufacturers are using increasing quantities of magnesium to reduce vehicle weight. Safe handling of combustible metal fires can greatly reduce the risks to your members and community.
LIKE PUTTING GASOLINE ON A FIRE
During my fire service career, I have seen numerous reports in which water was applied to try to extinguish well-involved combustible metal fires. Bright explosions that hurl burning molten metal hundreds of feet in the air onto emergency responders, equipment, and surrounding exposures make great images for the six o’clock news but do little or nothing to extinguish the metal fire. The profound reaction afterward is typical of emergency responders, “We were trying to accelerate the burning.”
That’s trueif you apply water to a combustible metal fire, you will accelerate burning. However, you’ll also add the potential for steam and hydrogen reactions and explosions. You will also significantly increase the risk of injury to fire crews. This is a very interesting concept, yet I’ve never heard of an IC ordering a gasoline tanker to pump fuel on a fire to accelerate burning.
This is exactly what you are doing when you apply water to a combustible metal fire. In simple terms, for every gallon of water you apply to a combustible metal fire, there is a potential release of hydrogen equivalent in energy to 0.43 gallons of gasoline. Every 100 gallons per minute of fire flow on a combustible metal fire provides the equivalent of 43 gallons of gasoline. You are also applying a significant amount of oxygen, which is also released to assist the burning (Table 1). It doesn’t make much sense to apply gasoline and an oxidizer on a fire you are attempting to extinguish.
COMBUSTIBLE METAL CATEGORIES
Combustible metals fall into four categories (Table 2). Alkali metals are water-reactive under nonfire and fire conditions. Applying water to alkali metals will result in fire and extreme reactions. In a nonfire situation, alkali earth metals, transitional metals, and other metals do not present the same hazards as alkali metals; but when burning, these metals can become extremely dangerous to responders if water is applied to extinguish fire. It is also important to note that most metals (such as iron) in a fine enough particle size will ignite and burn as well.
If not properly identified and handled, combustible metal fires present unique and dangerous hazards to firefighters. Most combustible metals involved in fire produce extreme temperatures ranging from 5,000°F to 8,500ºF. These temperatures result in the dissociation of water to its basic elements of hydrogen and oxygen. Application of CO2 has similar results with dissociation of carbon and oxygen.
These temperatures present extreme hazards to fire crews entering a structure where a combustible metal fire may be burning, with rapid heat buildup and fire spread characteristics. The temperatures encountered with a combustible metals fire will far exceed those for which structural and proximity fire gear are tested and will quickly burn through material if burning metal lands on it.
In 1989, the Seattle (WA) Fire Department experienced firsthand the dangers of a combustible metal fire burning in a structure: A lieutenant was killed. The fire cause was determined to be arson; a combustible metal was later determined to be a component of the accelerant. The ignition of the combustible metal created fire behaviors that were not expected for the type of structure involved. The structure became untenable within minutes, secondary to the rapid fire and heat buildup. Fire temperatures were estimated to be higher than 6,000ºF.
A burning combustible metal also produces a tremendous amount of smoke compared to other combustibles. One unique characteristic of a combustible metal fire is that the smoke is a white to grayish color if just the metal is involved. The smoke will also appear to be exiting the structure at a much higher velocity than you would expect in normal situations because of the high burning temperatures of the involved product.
Powders, dusts, chips, and swarfs (metallic particles and abrasive fragments removed by a cutting or grinding tool) of alkali earth or transitional metals present the greatest hazards to fire crews dealing with combustible metal fires. Powders and dusts are by far the greatest concern; they have a greater surface area and a high explosion potential should they become airborne in a natural environment or secondary to attempts to extinguish the fire.
(1) Titanium chip fire, Albany, Oregon. Photos courtesy of Albany (OR) Fire Department.
Aluminum powders have the highest KST rate (a measurement of inherent explosive power) of all the combustible metal dusts.
As a rule, larger products of alkali earth and transitional metals such as bars, ingots, heavy castings, and thick plates or sheets are virtually impossible to ignite; in most cases, they will self-extinguish when the heat source is removed.
(2) Aftermath of titanium powder fire, Albany, Oregon.
Fires involving large quantities of combustible metals are impossible to extinguish and are extremely difficult to contain if not caught in the incipient stage and controlled with a Class D extinguishing agent appropriate for the metal involved. In most cases, the heat generated by a metal fire will make it impossible to apply an appropriate agent to control the fire once it is beyond the incipient stage.
It is extremely important to conduct a good size-up and identify the combustible metals involved. The physical state of the product (e.g., chips, powders, fine dust), the location, and the quantity of product involved or potentially involved in the fire are important factors for responders to consider.
Obtain material safety data sheets (MSDSs), and consult people familiar with the product and its hazards. If you have combustible metal products in your response district, it’s extremely important that you become aware of that product’s specific hazards and the appropriate methods for dealing with them.
The only way to extinguish a combustible metal fire involving alkali earth metals and transitional metals is to provide an inert atmosphere of argon or helium, which in most fire situations is impracticable. Applying other agents will contain the fire until the metal has oxidized to a point at which heat production is reduced below the ignition point.
The standard extinguishing agents most of us use for ordinary combustible fires can be dangerous or ineffective on combustible metal fires. Table 3 provides a quick reference to common extinguishing agents and their ability to control a combustible metal fire in the incipient stage.
As a general rule, the best course of action is to allow the fire to burn itself out if the fire can be safely isolated. This may necessitate sacrificing the involved structure. Exposures and uninvolved product can be protected if adequate precautions are taken to ensure runoff does not reach the metal fire or, in the case of alkali metals, exposed metal not involved in the fire. It is also important to consider water sources within the structure that could allow water to reach the fire if breached. It may be necessary to isolate the domestic water supply feed to the fire area. Adequate preplanning would de-termine the valve locations.
In most cases, combustible metal fires will burn quickly and begin to develop an oxide crust that will limit open burning of the product. It is extremely important that the crust not be disturbed until the metal has completely oxidized to the point of extinguishment. Depending on the size of the fire, this may take 24 hours or longer. Thermal imaging can be a great asset in this case. Even though there may not be signs of external burning, the metal can remain extremely hot and continue to present thermal injury risk to responders and risks associated with application of water if the oxidized crust is disrupted prior to complete extinguishment.
Preplanning and having operating procedures in place for these fires are important for ensuring a safe outcome. Recent court actions in Ohio have questioned whether a fire department is immune from civil liability for applying water on a combustible metals fire when it has been made aware of the hazards of doing so.
Fires involving combustible metals can be safely and effectively handled when fire crews on the scene take appropriate precautions. Develop appropriate guidelines for dealing with combustible metals if they exist in your community.
National Fire Protection Association (NFPA) 484, Standard for Combustible Metals, is an excellent resource for facilities that use or manufacture combustible metals in your jurisdiction. The 2006 edition of the standard included a new chapter specifically related to fire prevention, fire protection, and emergency response. This will be extremely beneficial to emergency responders dealing with combustible metal incidents.
Author’s note: Carl Rivkin, staff liaison, and Tom Christman, chair, NFPA Committee on Combustible Metals, Metal Powders, and Metal Dusts, contributed to this article.
KEVIN L. KREITMAN is a 26-year veteran of the fire service and chief of the Albany (OR) Fire Department, which protects a city that includes three major facilities that produce combustible metals and products. He is a fire service member of the National Fire Protection Association’s Committee on Combustible Metals and is a graduate of the National Fire Academy Executive Fire Officer Program.