Using steel construction can significantly reduce the flammability of your structure. However, it doesn't make the building fireproof. Steel can be weakened and catastrophically fail if the temperature gets high enough. Steel loses nearly half of its weight-bearing capability once the temperature reaches 1100 degrees F (593 degrees C). Eventually, the structure will collapse, for one of the same reasons the Twin Towers collapsed on 9/11.
It may not have been possible to save those buildings and the people inside them, but you can substantially reduce the probability that your steel facility will suffer the same fate by using proven fire-resistant materials and following safety recommendations from authoritative sources.
AN INTRODUCTION TO FIRE RATING CONCEPTS
Fire ratings are developed using concepts meant to illustrate different risk areas from which fire damage can occur. The International Code Council and the Metal Building Manufacturer’s Association provide regulations and recommendations for creating a fire-resistant structure that meet International Building Code (IBC) and local fire codes.
Concept 1: Combustibility
The IBC recognizes that steel construction is non-combustible. It does not exempt steel structures from all fire protection requirements, although there are significant advantages for using non-combustible construction in comparison to combustible materials such as wood frame.
Concept 2: Allowable building height and area
Because steel is non-combustible and does not spread flames, your building is allowed larger and taller areas of non-fire rated (unprotected) in a steel building than if it was a wood frame structure. In fact, a steel building can have up to 50% more non-fire rated space than a frame built of combustible materials. Less need for fire rated protection lowers costs considerably.
Concept 3: Fire protection
Fire protection requirements are driven by four parameters:
- Intended end use of the building
- Construction type
- Occupancy type
- Site location
Intended use can impact fire protection requirements. Obviously, if you will be storing flammable materials, you will have more stringent requirements than if the materials were less likely to burst into flame.
We have already discussed construction type; steel is non-combustible and more durable in a fire situation than wood or plastic.
If the building is occupied, other fire regulations come into play such as the need for escape routes and recommendations on the direction the doors open. A different type of sprinkler system or flame retardant is allowed for human occupancy than for storage facilities.
Site location indicates how close the building stands to adjacent structures or property lines. The risk of fire spreading decreases with the increase in distance between structures. The larger the distance, the lower the risk, resulting in lower requirements for fire protection. If the building is constructed from steel, the requirements are further reduced.
Concept 4: UL ratings
The Metal Building Manufacturer's Association (MBMA) in partnership with Underwriter's Laboratory (UL) tested a range of fire rated assemblies for roofs, walls, columns, and joints. The result was two new UL ratings:
- UL Design No. W404 - One-hour exterior wall fire rating
- UL Design No. W413 - Two-hour exterior wall fire rating
These designations indicate that new exterior walls consisting of non-combustible metal building wall framing, steel furring, gypsum board, and exterior wall panels plus various insulation options meet one or the other of the UL ratings above.
The emphasis on energy conservation has an impact on insulation as well. Insulation must meet the energy code while meeting the fire code for the building to maintain its fire rating. W404 and W413 address flame and smoke propagation issues caused by the use of foam plastic insulation by allowing for energy code compliance using both fiberglass and rigid board insulation to achieve a fire resistive wall assembly rating.
Concepts 5: Fire rated materials
The most common material that meets fire rating requirements is gypsum wallboard. All MBMA rated designs use, at a minimum, generic 588-inch “Type X” gypsum wallboard, which is available from most suppliers.
Other fire-rated materials include:
- Concrete masonry for walls
- Spray-applied fire-resistive materials
UL ratings require special details for joints and penetrations that include intumescent fire caulks that expand in a fire to seal gaps or cracks, preventing the passage of smoke and flames.
FIREPROOF your metal building AT THE BEGINNING
Constructing a fire-rated building is easiest when fire-resistive materials are planned into the steel structural frame when it is built. To meet International Building Codes, a structure must be able to withstand two full hours of fire-strength temperatures before failure. The code specifies a range of fire protection such as sprinkler systems and other fireproofing materials, based on:
- Size of the building
The metal roof, walls, and flooring can be sprayed after construction since they need to meet less stringent standards. These areas may need to be recoated periodically to maintain the fire-retardant surfaces.
- Coatings and insulation types. A wide range of coatings and insulation can be used to make your building more fire-resistant. Only use materials that qualify for use under the fire-resistance rating of your facility.
The fire rating is based on the length of time it takes for protected metal to reach the critical temperature of 1000 degrees F (538 degrees C).
- Intumescent spray film coatings. An epoxy-like substance containing hydrates or chemically-bound water molecules that is sprayed on as a coating. Once dry it can be painted to match the surrounding areas. In the event of a fire, it swells and chars, releasing the hydrates to help the area cool and reduce surface conductivity, lowering the heat and reducing the lifespan of the fire.
- Endothermic fire proofing. An endothermic reaction is one that is accompanied by or requires absorption of heat. Mineral wool and ceramic fibers can be mixed into various building materials such as gypsum, resin, or concrete to provide fire resistant properties.
The materials are then added to steel structures as cladding or drywall. Onsite testing is recommended to ensure adequate fire protection since the added fibers can reduce material density, making it less effective.
- Mineral or high-temperature wool blankets. Similar to standard building insulation blankets, this type of fireproofing works in temperatures up to 2000 degrees F (1093 degrees C). The blankets may be encased in wire mesh and used in parts of the building that are out of sight, on curved surfaces, and where there is heavy foot traffic. They cost less than more sophisticated fire-resistance solutions.
- Application and maintenance. Fire-resistant materials are best installed by a professional. Request onsite testing of the products you select and schedule regular inspections, especially for hard-to-reach places. Budget for re-application of the materials as recommended by the manufacturer as they are not permanent. Exposure and general deterioration will render them less effective.
You are making an excellent start by constructing your building with fire-resistant steel but don’t stop there. Follow IBC and local fire codes to strengthen the fire safety of your building, its occupants, and its contents. A structure cannot be completely fireproofed, but you can make it as hard as possible for it to collapse.