How many columns must be thickness tested if there are 100 columns on a floor receiving SFRM?

In the context of testing spray-applied fire-resistant materials (SFRM) on structural columns, there are standardized requirements that dictate the number of samples or columns that must be thickness tested to ensure compliance with fire resistance ratings.

The correct choice reflects a common practice in quality assurance protocols, which may stipulate that a certain percentage of the total number of columns should be tested to verify the application thickness of the fireproofing material. When faced with 100 columns, testing 25 of them typically represents 25% of the total. This figure is strategic as it balances the need for comprehensive testing while minimizing the destructive nature of such tests on the overall installation.

Testing a representative sample ensures that the applied fireproofing meets the necessary thickness requirements across all columns, as variations in application techniques can lead to differences in coverage. This approach helps maintain the integrity of the building's fire protection system and provides assurance that if the tested columns meet specifications, the rest are likely to do so as well.

The other choices do not meet the usual standard for sampling size in this context, either being too low or disproportionately high for such a situation, which could lead to unnecessary disruption and material waste.