Mattresses have been around in some form or other since the dawn of civilization. However, it is only in the 20th Century that mattresses evolved becoming something much more than merely a cloth sack filled with natural cushioning, such as cotton or goose down, which our predecessors may have felt fortunate to sleep upon.
The modern mattress is often a very complex system of innersprings, coils, multiple layers of varying density foam products, and various synthetic material coverings to enclose and separate the inner workings. For the most part, many if not most of the materials of construction are synthetic products, typically polyester fabrics and polyurethane foams. And these synthetic products are all plastics of some form or another. A key feature in any mattress construction is the ability to include and entrain air in the product, most particularly foam products, and this provides cushioning effects we desire. Entraining air also has an unintended side effect for fire protection as it includes a ready mix of fuel and oxygen, both essential to the combustion process.
All of this is nice, but how does it relate to fire protection? Well, the first step in understanding how to protect something, is to understand, or classify, what it is. In this case, we understand that likely the largest component in a modern mattress is polyurethane foam, which is also classified by the fire protection industry as an expanded plastic, or as we’ve learned, a foam with air entrained. Therefore, the commodity classification of most all modern mattresses is an “expanded plastic” commodity.
Now to add another level of complexity, packaging. In sprinklered buildings, fires develop, or don’t develop, due in part to what starts burning first. Packaging can take many forms, including metal cans or drums, plastic cans or drums, fiberboard drums, plastic cases, wood crates, cardboard boxes, plastic bags, etc. By far the most common packaging in use today is cardboard boxes, which as it turns out have some very positive fire protection features.
Cardboard is an “ordinary” combustible with a relatively modest btu content per unit weight, and therefore burns with a moderate intensity as compared to plastics with a high btu content and a high fire intensity. And further, cardboard is a water adsorbent material which becomes difficult to ignite and burn once wet.
A fire involving commodities in cardboard boxes, even those filled with plastics will initially take on the burning characteristics of the cardboard packaging, and can be much easier controlled by fire sprinkler systems in this stage of development. Additionally, there is an added benefit that while sprinklers will operate over the fire area, they will also provide waterspray to immediately adjoining areas not yet involved in the fire. This will pre-wet adjacent cardboard boxes and inhibit their involvement in further fire growth.
Getting back to mattresses, they are NOT normally packaged in cardboard boxes, but are typically packaged in heavy plastic bags protecting the mattress from dirt, stains, water, etc. until opened by the purchaser. Obviously the plastic bags will also protect the mattress from sprinkler water discharge during a fire as well. Once the plastic bag is melted or burned away during a fire there is a fresh dry mattress available for contribution to the fire intensity, as opposed to a soggy cardboard box in the previous example. This knowledge allows us to further classify mattresses as a type of commodity with respect to fire protection. In this case, the mattress becomes not only an expanded plastic, but an exposed expanded plastic. This means that the surface is not available for pre-wetting from fire sprinkler systems, and has the effect of raising the underlying commodity to a higher level of fire hazard. The following is a list of general storage commodity classifications arranged in decreasing order with the highest fire hazard at the top;
|Exposed (Uncartoned) Expanded Plastics||MATRESSES|
|Exposed (Uncartoned) Unexpanded Plastics||hard plastic lawn furniture, unpackaged|
|Cartoned Expanded Plastics||Styrofoam ice chests in closed cardboard boxes|
|Cartoned Unexpanded Plastics||hard plastic products in closed cardboard boxes, such as children’s toys|
|Class IV||same as Class III, but with VERY limited amounts of plastic in the products, or in the packaging|
|Class III||paper, cardboard, wood, and ordinary combustibles|
|Class II||non-combustible commodities stored in multiple-thickness corrugated cardboard cartons, wooden containers, solid wooden boxes, or equivalent combustible packaging material on wood pallets|
|Class I||non-combustible, e.g. metal ceramic, glass, etc., products in single thickness cardboard cartons|
As can be seen, mattresses are at the very top of the list, requiring the highest degree of fire protection to control a fire. The degree of fire protection required will further be affected by the arrangement of storage (solid pile, racks, portable racks), the height of the storage (the higher, the bigger the fire), and the height of the building and clearance between top of storage and sprinkler heads (sprinkler designs create water droplets which depending on the sprinkler head can vary in size and fire penetrating ability).
Don’t remove this tag under penalty of the law! But aren’t mattresses designed to be fire retardant? Federal regulations 16 CFR 1632 and 1633, administered by the U.S. Consumer Product Safety Commission (CPSC), require all mattresses sold in the United States to meet flammability standards. To do this most manufacturers add fire retardant chemicals to foam formulations and also apply them to fabrics.
Doesn’t this mean that mattresses can’t burn??? One would think so, but it turns out the answer is not quite that simple. The regulations are established for consumer protection, and the burn test configurations simulate a single mattress as it would likely sit on a bedframe in your home. However, the tests are not intended to, and do not contemplate mattresses arranged as found in a warehouse environment. Think of it as akin to a single log in your fireplace, and it would be a difficult trick to get one single log lit and burning. But surround that log with lots of other logs, there is no trick at all, and igniting and burning this configuration becomes easy.
To respond to this scenario, the fire protection community has adopted a generally conservative stance with respect to goods and materials which are “fire retardant”, and this includes mattresses. In warehouse or storage arrangements fire retardant products are treated as if they are identical to the same materials without fire retardant properties. A general exception is if large scale fire testing has been successfully performed. However, large scale testing is most often impractical due to the high costs involved.
Prior to the 1980’s, the only options for protection of mattresses was from traditional ceiling sprinkler heads, and where rack storage was involved, almost always in combination with in-rack sprinklers. A properly designed ceiling sprinkler system in combination with in-rack sprinklers has proven to be highly effective in controlling fires involving mattresses. However, with in-rack sprinkler designs there are a few difficult issues. Mattresses come in a wide variety of sizes which are most frequently mixed, thus they create an irregular storage arrangement that permits enhanced fire growth. They tend to be very saggy and will droop from one storage position to the next, particularly in a mixed array. In rack storage arrangements, this tends to obscure the flue spaces between the backs of the racks (longitudinal flues) and at the horizontal uprights between the rack sections (transverse flues). Maintaining these flue spaces is critical for successful fire protection as it permits sprinkler water to penetrate through the rack and reach the seat of the fire. Additionally, in-rack sprinklers are located in flue spaces and are subject to frequent damage from handling of mattresses into and out of the racks.
In the 1980’s the advent of new sprinkler technology, known as ESFR (Early Suppression Fast Response) sprinklers began to be a game changer. Initially there were limited, to no options for protecting high challenge mattress storage, however over time technology and understanding has improved and there are now several ESFR type technologies which can provide adequate protection without the use of problematic in-rack sprinklers.
One of the key issues with ESFR type sprinklers to protect mattresses remains the proper layout of racking systems to allow for the consistent presence of both longitudinal and transverse flues within the racks. Risk Logic consultants are well versed in these issues and are available to provide assistance in the design and layout of sprinklers and storage solutions.