Limiting temperature method

(the limiting temperature) with the temperature of the hottest part of the section at the required fire resistance time (the design temperature). In BS5950 Part 8 this is done via a set of prepared tables and is illustrated graphically, Figure 35 shown below. If the limiting temperature exceeds the design temperature no protection is necessary

This can be of particular value when assessing whether unprotected steel will achieve 30 minutes fire resistance without protection. It can also be of value when calculating failure temperatures to assess how much fire protection is required for higher periods of fire resistance.

For example, if it can be shown that the failure temperature is (say) 700°C rather than 620°C, significant reduction in fire protection thickness may be possible. This can be  important for intumescent coatings, especially at high fire resistance periods. It is unlikely to provide any value when using board or spray fire protection.