Fireproofing steel is all about time. Increasing the fire resistance of your structural steel through fireproofing buys you time—time to evacuate, time to fight the blaze, time until the total collapse of the structural steel in your facility.

Making sure your fire resistance measures are up to code is paramount to obtaining insurance and promoting the safety of facility workers. And, in industrial facilities such as refineries and plants, fireproofing steel is critical to protecting your facility from total failure in the case of a fire.

There are many standard test specifications on which fire resistance is measured. Chances are, though, if you’re dealing with steel, you’ll need to meet ASTM E119, NFPA 251, UL 263 or ISO 834 standards. An experienced coatings contractor should be able to steer you to the correct standard and coating for your particular needs.

How fire resistance ratings are determined

No matter the standard, the key to fireproofing steel properly is ensuring that fire resistance (the ability of your structural steel to resist spread, collapse and failure exceeds) fire severity (a measure of the temperature of a fire and the impact it might have on the material) for a specified amount of time. 

There are three units used to compare fire severity with fire resistance to obtain a fire resistance rating (FRR): time, temperature and strength. Time is specified as the time until failure; temperature as the temperature required to cause failure; strength is specified at the load capacity at a certain temperature. Regardless of which unit is used in testing, the FRR is typically measured in minutes or hours until failure.

Usually, an FRR for a particular coating is decided upon by subjecting structural steel coated in the product to a test fire. The time-temperature curve for the test is then compared to the standard, say, the ASTE E119, and an FRR is assigned to a particular coating. 

Fire resistance tests can be performed on either the small or the large scale. They are, however, usually performed on a large scale, because it allows for judgments to be made about the method of construction, thermal expansion, bending and shrinkage. Large-scale tests offer more realistic results and more realistic ratings.

How to read a fire resistance rating

To understand how to interpret an FRR, you must first understand what constitutes failure in a rating test. If, for instance, you need to meet an FRR of 90, your steel must be able to resist fire in three ways—stability, integrity, insulation—for the entirety of those 90 minutes.

To pass the stability test, your structural steel needs to continue to bear loads for the duration of the test. Integrity refers to a material’s ability to stay intact, with no fissures or cracks, as to contain the fire. Insulation refers to the steel’s ability to slow the spread of heat from one side to another; in the case of a fire, this would serve to prevent spread. An intumescent coating can go a long way toward increasing this rating on structural steel.

Essentially, to receive a fire rating of 90, a coating needs to help steel maintain function and prevent spread for the full 90 minutes. Lately, fire codes have begun to individually specify FRR based on these three variables—this is why you see some FRRs broken up into three (i.e., 90/90/90) in the order of stability, integrity then insulation. For non-load bearing walls, a fire-code might specify an FRR of -/90/90, meaning that an FRR for stability is not required.

No matter what code you need to meet, an experienced contractor will be able to guide you in the right direction. Fireproofing steel is crucial to keeping your facility functioning and your insurance rates low. 

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Fireproofing steel: A guide to fire resistance ratings
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