Selecting the right fire protection for a steel section is essential. Too much protection can be expensive, and too little can be dangerous. Use these 3 steps below to choose the correct protection.
1. Check the Steel Section Without Protection
Start by checking the steel section without fire protection. Determine the reduction factors based on the fire type and duration. Use the reduction factors to calculate the section’s capacity in the fire state.
If the section is overutilized it is necessary with fire protection. And to determine how much protection is needed the critical steel temperature first needs to be determined.
If the section capacity is insufficient, fire protection becomes necessary. The critical steel temperature determines the required amount of fire protection.
2. Calculate the Critical Steel Temperature
Calculation of the critical steel temperature is an iterative process. Start by guessing the critical steel temperature. Then determine the reduction factors and calculate the utilization. This process continues until it reaches a temperature that results in 100% utilization. This is the critical steel temperature. Software like PolyBeam and PolyColumn will do this process for you.
Avoid using simplified methods as they may be too conservative.
3. Select the Appropriate Fire Protection
There are two main types of fire protection for steel: fire paint and fireboards.
Fire paint is cheap, keeps the steel’s raw look, and is usually applied before the steel arrives on-site.
Fireboards offer more protection and work well for on-site welding or adjustments.
Most manufacturers offer design tables to help pick the right amount of paint or boards. To use these tables, you need to know:
- The fire time.
- The critical steel temperature
- The section factor
The section factor is the surface area of the section exposed to fire divided by the volume (Aₘ/V). Software like PolyBeam and PolyColumn will give you this value.
Below is an example of how to use a design table from Scandi Supply. A HE260B section exposed to a 60min standard fire. And with a critical steel temperature of 600 degrees.
In this case, the steel needs 0.752mm of paint or 22mm fireboard for protection.
Nullifire SC902 Fire Paint
FireFree® ScandiBoard 850
Fire Design with PolyBeam and PolyColumn
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