STORAGE PRACTICES IN WAREHOUSES AND DISTRIBUTION CENTERS
BY GERARD J. NAYLIS
Fires in storage occupancies (warehouses, distribution centers, storage buildings) present unique challenges to firefighters. The growth, development, and behavior of any fire in a storage occupancy will be influenced by a number of factors. Firefighters need to know what these factors are and how each will influence the fire.
CLASSIFICATION OF THE COMMODITY
The first factor to consider is the classification of the commodity or product being stored. A commodity`s classification provides firefighters with a relative understanding of its heat release rate and potential burning characteristics. Two generally accepted documents that provide guidance to commodity classifications are National Fire Protection Association (NFPA) 231, Standard for General Storage, and Factory Mutual Engineering`s Data Sheet 8-0, “General Storage Practices.” Although these documents provide a great deal of guidance for determining a product`s commodity classification, the best way to ensure that you are assigning the right commodity classification is to subject the product to a fire products collector test to identify the heat release rate of a given product. Once known, a fire protection system that will provide an adequate level of protection against the fire challenge represented by that particular product can be designed and installed.
The commodity classification of most products is based on the product`s combustibility and packaging material. Products are segregated into one of the four general classes of commodities. There are separate commodity classifications for plastics, aerosols, and flammable liquids. There are also special classifications for unique types of commodities such as roll paper and rubber tires.
Class I. This class of commodities includes products with little or no combustible packaging (noncombustible materials on wood pallets). This class commonly includes building materials such as concrete blocks, steel beams, and metal pipe and tubing; heavy machinery; glass; and rock or stone.
Class II. When Class I commodities are placed into combustible packaging, they are then considered Class II commodities. Examples include household appliances placed in triwall corrugated containers. Although the appliances themselves are not considered to be combustible, the triwall corrugated box is; it increases the fire hazard. Products shipped in enclosed wooden crates are also considered Class II commodities.
Class III. This class covers combustible commodities typically packaged in combustible packaging, including paper and paper goods, natural fabrics, food products, wood furniture, and similar types of products that might be considered ordinary combustibles.
Class I, II, and III commodities may contain up to five percent plastic by weight or volume.
Class IV. This includes products for which the quantity of plastic exceeds five percent but is less than 15 percent by weight or 25 percent by volume. Note that a commodity`s classification includes not just the product itself but the product and the packaging material. The reason for this is the plastic`s heat release rate that has now been introduced into the commodity.
According to Factory Mutual Engineering, if a product that has more than 15 percent of plastic by weight or 25 percent by volume, the entire product should be considered a plastic.
Groups of Plastics
Plastics are broken down into groups A, B, and C.
Group A. Typical examples of Group A plastics include those that are blown, foamed, or expanded. Examples include disposable hot beverage containers, disposable dishware, building insulation material, meat trays, and packing material. These plastics have a very high heat release rate compared with ordinary combustibles (20,000 Btus per pound vs. 8,000 Btus per pound).
Group B. These plastics are typically the soft, pliable items that include plastic film and wraps, garbage bags and garbage pail liners, plastic utensils, plastic tubing such as that found in the medical industry, and certain types of rubber.
Group C. This group includes high-density and high-impact types of items, including toys, appliance shelves, and ashtrays. Although Group C plastics are more difficult to ignite, once they begin burning, the heat release rate is greater than that for ordinary combustibles.
AEROSOLS
Aerosols are broken down into three categories or levels: 1, 2, and 3.
Level 1. Included are water-based products such as shaving cream, spray starch, and air freshener.
Level 2. Included are alcohol-based products such as hair spray, deodorant, and many health and beauty aids.
Level 3. Included are petroleum-based products such as spray paint, degreasers, and many automotive care products.
Characteristics of Aerosols
Regardless of the type of product contained in the can, all aerosols share certain characteristics. The first is that they are all under pressure. When heat is applied to the cans, there is the potential for a BLEVE (boiling-liquid, expanding-vapor explosion) and for the cans to rocket over great distances.
The other characteristic is the propelling agent within the canister. Prior to 1989, many aerosols used some type of chlorinated flurocarbon (CFC). Production of these types of gases was essentially halted in the United States and other countries as a result of the Montreal Protocol of 1989. Manufacturers turned to more environmentally friendly types of gases–such as propane, butane, and isobutane–to propel the aerosol products.
The third characteristic shared by aerosols is that most, if not all, aerosol cans are transported in corrugated boxes. In a fire situation, the packaging material burns, and the heat is transferred to the metal aerosol cans. When an amount of pressure sufficient to cause the can to rupture develops, the cans–particularly in Levels 2 and 3–will rocket over great distances and trail burning product aerosols. These rocketing aerosol cans represent a significant hazard to firefighters.
Aerosol Packaging and Cushioning
Packaging and cushioning materials also figure into a commodity`s classification; they may contribute to the commodity`s potential to spread the fire or inhibit firefighting. The typical cushioning material used to protect items years ago was newspaper (shredded or bailed up) or cellulose. Today, plastic peanuts or bubble wrap is used. Some larger items use foamed, blown, or expanded plastic to protect the product and hold it in place–even better, the plastic can be fit to the box in which the product is being sent. All of this contributes to an increase in the amount of plastic in the commodity and, therefore, increases the heat released by the commodity.
Encapsulation. In the past, boxes were held on pallets by steel banding. Although the steel bands were very effective at securing the boxes on the pallet, they were difficult to remove and presented a potential cause of worker injury. Once again, the plastics industry came to the rescue. In today`s warehouses and distribution centers, most pallet loads are held in place with a variety of shrink-wrap plastic film–a group B plastic. In some cases, the pallet is encapsulated in the plastic–that is, it covers the top of the pallet as well as its sides. Encapsulation affects the ability of the fixed fire protection system to control a fire, because the sprinkler water cannot prewet the combustibles near the fire (the plastic wrap sheds water). As a result, more of the contents will become involved in the fire. Firefighters` hose streams will not be able to prewet the combustibles either. The water supply must be increased if firefighters are to have any chance for success.
Plastic bottles. The introduction of plastic bottles has also had a major impact from a firefighting aspect. Flammable and combustible liquids that previously were marketed in metal cans (charcoal lighter fluid, for example), glass bottles (vegetable oil), or fiberboard containers (motor oil) are now almost exclusively sold in plastic bottles, which meet consumer needs for nonbreakable packaging and reduce manufacturers` costs. Fire departments, however, have had to learn the hard way that these plastic containers lose their structural integrity at very low temperatures, allowing product to escape and permitting a pool fire of burning liquid product to develop. As more liquid escapes and sprinklers activate, the fire spreads as burning liquid lies on top of the sprinkler water that makes it to the floor. An excellent case in point was the Sherwin-Williams Distribution Center fire that occurred in Dayton, Ohio, in 1988.
The unfortunate truth is that unless a fire involving flammable or combustible liquids in plastic containers is knocked down while the fire is still developing in packaging material, the fire department likely will not be able to stop the fire from consuming the entire building. Once a well-sustained liquid pool fire is burning, the only thing the fire department can do is to consider a very large foam attack. Barring that, firefighters are left to perform exposure protection.
SPECIAL-RISK COMMODITIES
Some commodities are treated as unique and special risks. This group includes flammable and combustible liquids packaged in containers that are not plastic, roll paper, nonwoven products, and rubber tires.
Also, unusual or unique operations involving ordinary commodities require special attention. Some examples are storage or salvaging facilities for scrap paper, wood chips, and stumps and recycling facilities. The most important thing to remember is that each of these facilities has its unique hazards and needs to be approached as a different scenario during a fire.
STACKING ARRANGEMENTS
Products in warehouses and similar buildings are stacked and arranged by a variety of methods. When most storage was moved by hand, goods were stacked on the floor up to heights that could be reached while standing on the floor or when using a small stepladder. This type of storage is known as solid pile. If the boxes are placed on pallets, either to keep the storage off the floor or to allow it to be moved more easily, the storage is considered palletized.
After World War II came the forklift and rack storage. Boxes were placed on wooden pallets, which in turn were placed in the racks. Initially, these racks went up as high as 20 feet. Today, it is common to find rack storage of 35 and 40 feet. In some places, rack storage can be found as high as 100 feet.
Racking styles. Rack styles include single row, double row, and multirow. Single-row racks, as the name implies, are a single pallet deep and typically are four feet across. In a double-row rack, two single-row racks are joined together; a six- to 12-inch flue space is between the two racks. When a double-row rack is greater than nine feet across, or if three or more racks are joined together, the rack arrangement is considered multirow.
Another type of arrangement is the cantilever rack. These racks have a solid beam that rises in the center and arms that extend outward. They are found in lumberyards and warehouses that store carpet as well as in facilities where unimpeded access to the underside of the storage is necessary. These racks may also be found in boatyards and boat-manufacturing facilities.
Regardless of the type of rack, all will hold the storage in place while it is burning. Racks also permit the maximum surface areas of the storage to be exposed in a fire, permitting the fire to transfer the greatest amount of heat possible. The commodities heat up more quickly and become involved faster.
Solid shelving. The absence or presence of solid shelves has a tremendous impact on the burning characteristics of the commodities stored in the rack and on the response of the fixed fire protection. In some cases, solid shelves are installed in conjunction with in-rack sprinklers, to assist in containing a fire. When solid shelves are installed without in-rack sprinklers, water from ceiling sprinklers is shielded from reaching the fire, allowing the fire to grow and spread. Eventually, the fire will begin to jump from rack to rack as a result of radiant heat transfer and overwhelm the fixed fire protection.
PREPLANNING CRUCIAL
Knowing what types of commodities are in a warehouse or distribution center is of critical importance if the fire department is to have any chance of controlling a fire in one of these facilities. The fire service has several mistaken beliefs when it comes to these buildings.
Myth 1. If the building has sprinklers, the fire will be controlled, and all will be well. The sprinklers will control the fire only if the water supply and sprinkler design are matched to the fuel load (occupancy) and its stacking arrangement. Think of it this way: The sprinklers are the checkbook, and the water supply and system design are the money. If you try to cash a check for more than the amount of money available, the check will bounce. In our example, the building will end up burning to the ground.
Myth 2. The property insurance company will force the building owner or tenant to upgrade the protection or will cancel the insurance. Wrong. The fire insurance industry is a business, and the companies that make up that industry make business decisions every day. If the market is soft and competition is stiff, many fire insurance companies will recommend–but not require–that protection improvements be made. If the protection is inadequate, a fire insurance underwriter will most likely buy reinsurance to protect the company`s assets or limit the amount of insurance provided. Either of these moves does little to help the fire department when the building is on fire.
Because of these myths, fire departments develop a false sense of security, believing that even if a fire call comes in for a warehouse or distribution center, there is nothing to worry about. Nothing could be further from the truth! Fire chiefs would be better served by recognizing the rapidity with which a fire in one of these buildings will spread due to–you guessed it–the type of commodity and the manner in which it is stored.
The fire department needs to know how the various commodities are moved from one place to another in the building. Fifty years ago, workers moved and handled most boxes. Today, state-of-the-art forklifts and conveyor belt systems use electric eyes that read bar codes attached to the boxes holding the commodities. Depending on the arrangement of the operating system, the conveyor belts could spread the fire rapidly throughout the building before the first fire department unit arrives.
The incident commander must remember to secure all conveyor systems in place on arrival. Knowing which commodities are present in a warehouse or a distribution center and how they are stored will greatly enhance a fire department`s chances of controlling a fire in these occupancies. Confirm these storage practices for all storage facilities at least annually. n
n GERARD J. NAYLIS has been a volunteer in the Bergenfield (NJ) Fire Department for 26 years and previously had been a career firefighter in the Atlantic City (NJ) Fire Department for 10 years. He is the second vice president of the International Association of Arson Investigators, a member of the Arson Conference Planning Committee at Rutgers University in New Jersey, and a member of the Bergen County Juvenile Fire Prevention Program Advisory Board.
