Fireproofing refers to rendering something fire-resistant or incombustible. It could be an entire structure, a specific material or some building components. This is considered a passive fire protection measure.
There are several fireproofing methods used in construction. However, it is important to note that items classified as “fireproof” are resistant to a specific circumstance. In other words, the item may be damaged by fire that exceeds the intensity or duration for which it was designed.
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Fireproofing in Steel Frame Construction
Structural steel melts at approximately 2,500°F, while building fires commonly reach a temperature in the range of 2,000°F. The possibility of melting steel is rare, but this does not mean that steel structures are safe. Consider that the material deforms and loses strength when exposed to high temperatures. Building codes require fireproofing protection for structural steel as a safety precaution.
Fireproofing steel will ensure a building keeps its shape in the event of a fire, allowing people to escape during an emergency. Commercial structural steel should meet at least the 2-hour fire resistance rating, among other requirements. The common ratings are 2-, 3-, and 4-hour marks. Certified AISC structural steel fabricators are qualified to meet fireproofing needs.
Method for Fireproofing Structural Steel
The most common way of fireproofing is by spraying low-density fibers or cementitious compounds, called spray-applied fire-resistive materials or SFRM. These sprays can be applied wet or dry, in coatings of the desired thickness, to provide heat resistance to steel. However, they are also used in wood, fabrics, and other materials. Even though sprays are the most common, they are not the only choice, and this section will describe other options.
These coatings are also known as intumescent paints, and they provide fire resistance to steel members. Intumescent coatings can expand as much as 100 times their original thickness, providing greater resistance by creating a buffer between a steel element and the fire. The coatings will undergo a chemical reaction and expand when exposed to extreme heat. This product is applied just like paint, and commonly used in steel exposed to the general public.
Flexible Blanket Systems
Flexible blankets are designed for specific needs and can be used as fireproofing material. The method is very practical, but there is a limited number of manufacturers. This method meets almost all safety standards and codes. It provides a reliable barrier to prevent fires from spreading to structural members, while maintaining a toxic-free environment.
Rigid Board Fireproofing
Rigid board fireproofing is available in different thickness, and can be easily installed during the process of installing steel decks and beams. These boards are moisture-resistant and provide fireproofing, thermal insulation and acoustic control, while preventing pest attacks.
Concrete nowadays is less popular as a fireproofing material for steel, and it is mainly used to encase large sections of steel. This requires more space that other options, due to the volume of concrete used. Also, this is not as aesthetically pleasing as other options, so it is used in places where appearance is not a main concern.
On-site Fireproofing of Steel Elements: Hazards and Drawbacks
Fireproofing steel elements at the construction site should be avoided at all costs. It will delay production and can also be a health hazard for employees, especially with fireproofing paints or sprayed fire-resistive materials.
To activate the paint, the chemical mixture is exposed to extreme heat, which releases toxic vapors. This method does not require a column cover, making it more appealing than spray, but the vapors can be hazardous to the user and surrounding workers.
SFRM includes ingredients like gypsum, carbon black, and cement. These materials are usually mixed with highly reactive chemicals to accelerate the hardening process. Those chemicals are very dangerous for people, possibly leading to sinus infections, lung cancer, and other respiratory issues.
Fireproofing on site will generate construction delays, regardless of whether a fireproofing specialist or the construction team performs the job.
- Employees will have to maneuver around the jobsite.
- Areas will need to be blocked to avoid someone bumping into wet foam or paint, and materials need to be completely dry before final installation.
Another drawback is the additional supervision required to ensure proper fireproofing, which is not necessary when elements are made by certified fabricators off-site.
In a fire outbreak, structural steel fireproofing can make the difference between the entire building structure sustaining damage and a complete collapse. Passive fire protection acts as a complement to active measures such as fire sprinklers, making buildings safer for occupants, while protecting the owner’s investment.