Fuel For The Fire
March 25, 2008
News stories pertaining to fires inevitably contain a phrase similar to: “when the flames subsided…” Everyone knows what happened at that juncture - the fuel had run out because a fire had just consumed every bit of it, and there was nothing left to burn. A familiar saying known to Navy and USAF fighter pilots goes like this: “The only time you have too much fuel is when you’re on fire.”
This clever adage also is sound advice for the facility manager of an industrial or storage warehouse. The analogy is that inside a facility without fuel, fire cannot burn. With an abundance of fuel, the potential exists for a fire to rage uncontrollably. The chance for a fire to begin, how quickly the fire spreads, and how destructive the fire can ultimately become depends upon an informed and close examination of the fuel itself.
Suppose that your place of business experiences a fire. It is likely what burned in this scenario were either solids or flammable liquids. In the aftermath of an actual fire, various business personnel will be asked a number of questions, most of which have to do with “property” (i.e., the commodities that were contained in their place of business). An accounting will be requested - a succinct catalogued recording of everyday items that the firm uses in any quantity that may ignite when fire or sufficient heat is present.
In a perfect world, an inventory of this type should have been formulated as part of a total preventative firesafety effort. Building engineers must be aware of how toxic, flammable, explosive, reactive, radioactive, or corrosive the building contents are by nature, and in combination with other materials present. For any facility, the most important information that can be supplied to firefighters involves the identification of existing hazardous materials. Interaction with local fire officials also gives you the following to think about in terms of a potential fire:
· What are the potential sources of ignition?
· How fast will the fire grow?
· Will the alarms respond rapidly?
· Where are the optimum paths of egress?
· What effects will the resulting smoke have on life and property?
· How can the fire be controlled?
The conditions under which the Incident Commanders and the Hazardous Materials Control Officers of any organized firefighting team attempt to control and mitigate incidents involving hazardous materials are often unpredictable and always very stressful. Because of these difficulties, the effectiveness of their strategies and tactical decisions are highly dependent on the integrity, quality and accuracy of the information provided to them.
When we concern ourselves with the fire hazards of solids and liquids (and dusts and gases) present in any building, we need to investigate the volatility of these materials because their fire potential differs considerably due to variations in burning characteristics. The most important items to spot, of course, are those that represent the greatest threat. To measure and identify those that are the most menacing to your business, the following three factors must be considered: the flash point of the material, its ease of ignition, and its ignitability limits.
SolidsThe volatility of any solid, and that includes the structural building materials (wood, steel, concrete), can always be tempered to some extent by flame-resistive treatments and/or fireproofing. What makes a solid most susceptible to combustion is the amount and degree of heat that is applied to its surface over a certain duration of time. With proper flame-resistant treatments, flame spread can be effectively diminished even if ignition has already occurred, thereby depreciating heat release rates. This is especially true when the material is wood.
When the potential combustible is a stored commodity as opposed to a part of the building structure, there is limited “fireproofing” potential. Realistically, we cannot fireproof everything in the warehouse - this is the basic reason for installing automatic fire suppression systems. Far from being a stopgap measure, fire sprinkler systems are designed to control or extinguish fire by a design in congruence with the existing commodity hazard and conditions and arrangements of storage. This sprinkler system design and its accompanying water supply is bolstered to a recommended minimum degree to protect products with higher burn rates, such as rubber tires, roll paper, certain plastics, and upholstery containing plastic foam.
Most plastics, when stacked in storage warehouses, will burn at the same rate as stored cardboard boxes, fabrics, and wood. What burns much more intensely is foam rubber and foam plastic, which will also produce a virtual cloud of smoke and toxic gas. When used as wall or ceiling insulation, foam plastics are covered and concealed by gypsum wallboard, which constitutes a fire-resistant barrier.
This effective fire solution is not an option when dealing with storage racks filled with mattress pads or furniture cushions. Buildings that warehouse these items, or highly flammable products such as tires, plastic packing, plastic insulation, roll paper, furs, or cellulose nitrate film, will require the installation of smoke and heat vents.
As with the increased capability of the fire sprinkler system, the number and size of the vents must be specifically tailored to the anticipated storage height and the quantity of the commodity that is present. You cannot play poker with this: It is a necessary life-safety measure, as well as an aid to the responding firefighting team.
Specifics for the classification of commodities are found in NFPA 13. Table A.5.6.3 offers an alphabetized commodity listing to identify the corresponding hazard group category. Products to be stored higher than 12 feet are designated by one of four classifications: Class I being the least volatile, Class IV being the highest. They are further established as follows:
Class I - encompasses essentially noncombustible products in paper or cardboard cartons or wrappings, with or without wooden pallets.
Class II - is composed of Class I products in wooden or multilayer cardboard containers, with or without pallets.
Class III - contains wood, paper, or natural cloth products or Group C plastics, with or without pallets. A limited amount of Group A or B plastics may also be included.
Class IV - is composed of any of the above, with an appreciable amount of Group A or B plastics in ordinary corrugated cartons, or with Group A or B plastic packing, with or without pallets.
Fast-developing, intense fires can result where large quantities of plastics or rubber are stored. Those commodities are classified into groups (A, B, or C) with Group A representing the most difficult of the potential fires to combat. Examples of specific Group A commodities are listed in Table 18.104.22.168 of NFPA 13.
The next tables in succession note the appropriate classification of Group B and C plastics and rubber by material composition. For example, ethylene fluoroplastics and silicone rubber fall into Group B, PVC (polyvinyl chloride) and polyvinyl fluoride fall into Group C, while polyethylene, polypropylene, and butyl rubber fall under the Group A category.
The suppression of any fire involving these solids will be best accomplished with large volumes of water. Water-based portable extinguishers (Class A or Class ABC) must be present, and in-place standpipe and sprinkler systems must be specifically designed for each storage arrangement.
It is extremely important to recognize that any fire involving plastics or rubber can and will generate a prodigious amount of dense, toxic smoke. The entire building must be immediately evacuated and responding firefighters should be forewarned of the respiratory danger.
It is critical to recognize materials of which it is not advisable to use water as an extinguishing agent. This is very important when certain chemicals are involved. For example, the application of water on quantities of aluminum powder, calcium carbide, calcium phosphide, metallic sodium and potassium, quicklime, magnesium powder, and sodium peroxide may pose a dangerous threat to personal occupant safety and will do nothing towards the termination of fire.
The chemical properties of all materials must be reliably established. Certain chemicals actually have the ability to oxidize other materials. Specific chemicals that have toxic, combustible, unstable, or reactive properties must be handled within a closed system. The insurance carrier of any business employing the use of these chemicals will certainly provide a long litany of control and protection requirements.
LiquidsThe specific flash point of any liquid is what is used to differentiate flammable from combustible liquids. By definition, a flash point is the lowest temperature at which a liquid gives off enough vapors to ignite momentarily in air. In the presence of flammable vapors, rising heat, a spark, or some other source of ignition will be enough to quickly start a blazing fire or in some cases (when in a confined space) an explosion.
A flammable liquid (classified as a Class I liquid) is any substance that is in liquid form at ordinary temperatures and possesses a flash point below 100°F. Gasoline is one common example of a flammable liquid. Just in U.S. residential homes, there are more than 5,000 gasoline fires annually, resulting in approximately $100 million in direct property damage. Gasoline is extremely volatile and must be stored in small amounts in separate “cutoff” rooms. The smaller the containers, the better. Liquid containers of five gallons or less, called safety cans, are virtually leakproof and provide a means of safely transporting the liquid. In addition, the containers:
- Contain automatically closing fill and dispense openings.
- Vent excess pressures to ward against vapor explosion.
- Prevent external flames from coming into contact with the liquid.
- Clearly mark the container contents.
- Will bear a U.L.- or F.M.- approved designation.
All flammable liquid containers are to be kept in a remote location, within a metal cabinet or “flammable liquid locker” designed specifically for this purpose. The containers should be marked with one of the following subclassifications:
Class IA: Liquids with flash points below 73°F and boiling points below 100°F.
Class IB: Liquids with flash points below 73°F and boiling points above 100°F.
Class IC: Liquids with flash points above 73°F and boiling points below 100°F.
A combustible liquid has a flash point equal to, or above, 100°F. These are subdivided as follows:
Class II: Liquids having flash points between 100°F and 140°F.
Class IIIA: Liquids having flash points between 140°F and 200°F.
Class IIIB: Liquids having flash points in excess of 200°F.
The reasoning behind such well-defined category delineation is for code compliance and suppression system design. As shown in Table 1, hazard control measures are taken to much more stringent levels based on the degree of hazard and the total amount of liquid to be stored and handled.
Most facilities utilize flammable and combustible liquids to some extent in everyday operations in the form of solvents, lubricants, grease, and fuels. Some are contained in aerosol cans, which pose their own special threat. The most fundamental safety measures to be taken consist of keeping the liquids in closed containers as much as possible to minimize their exposure to air. They should also be kept a reasonably safe distance away from electrical and heat-producing equipment.
Fixed fire suppression systems must be well-maintained, annually tested, and designed in accordance with the recommendations noted in NFPA 30, Flammable and Combustible Liquids Code. The best fire extinguishers to mount nearby are either foam or BC-rated dry chemical extinguishers. Other recommended safety measures include:
• Explosion venting of specially designated rooms (especially essential for Class 1A and other unstable liquids).
• Restrictions on liquid quantity within the building and in individual stacks.
• An abundance of air movement (mechanical ventilation).
• If possible, the alternate use of nonflammable liquids (two cleaning solvents that are nonflammable at normal temperatures are trichloroethylene and tetrachloroethylene).
• Operations training of personnel.
•Safe handling and manufacturing practices.
For optimum hazard control, dispensing and storage operations of flammable liquids are best kept in a building outside of the plant, or in a vented “cutoff” room attached to the plant. The guiding principle here is to allow for the escape of flammable vapors. Also, any fire occurring within the cutoff room will be reasonably contained and unable to spread to other areas of the building.
Fire hose stations should be in close proximity. The cutoff room must have self-closing doors and a drainage system, usually incorporating a lower (6 in. or greater) floor with scuppers to direct the flow of spilled liquids to areas other than the adjacent facility. It is an unwise practice to keep more-volatile liquids in storage than is actually necessary for normal plant operations.
Any large fixed equipment such as commercial presses that are typically covered with an oily buildup should be protected by a separate (foam) deluge system. This is especially important when there is a pit beneath, since vapors from the oils and lubricants tend to lay in low areas and accumulate at dangerous levels. There are many NFPA standards that cover requirements and recommendations for specific industrial applications.
Finally, there is the matter of the disposal of hazardous waste that contains toxic, explosive, corrosive or flammable substances. These include (but are not limited to): paints, polishes, lacquers, solvents, automotive fluids, paste waxes, kerosene, turpentine, insecticides, chemicals, petroleum products, inks, varnishes and stains. Leftover hazardous products are not to be poured into open drains or onto the ground, and must be managed in accordance with approved safety and environmental regulations.
Today, permanent hazardous waste collection facilities dot the landscape of the United States and other countries, so there is little excuse for lackadaisical activity in this regard. Facilities also must be kept clean and free of combustible rubbish. Safe areas must be designated for the temporary storage of waste products. These products are not to be mixed and must be removed at regular intervals.
If “leftover” hazardous products cannot be used up in the plant, and have to be discarded in some fashion, a portable (wheeled) solvent tank may be used to transport the liquids. This tank also must be vented to avoid an excess of vapor concentration. While this might entail some degree of risk, it is infinitely more efficient, and perhaps less risky, than taking many small containers to the same destination.
Areas red-flagged as known hazards will certainly come into the sphere of influence of an insurance carrier or alert fire inspector. Activities such as paint or ink mixing, oil refining, chemical processing and/or plating, varnish dipping, solvent cleaning, and asphalt saturating inherently possess the need for high-hazard technical assistance. Applicable NFPA standards provide strict safety guidelines.
The “any protection is better than nothing” theory makes little sense when hazardous materials are involved. When the uninformed take shortcuts with regard to prevention and control in these situations, they are fighting a battle with outdated weapons. Only in code-compliant buildings of fire-resistive construction, protected by in-place fire suppression systems, that practice scheduled inspection and maintenance procedures, can we assume a reasonable measure of well-being.