FIRE SAFETY INACCURACIES MUST BE CLEARED UP
The intent of Nick Bernabé's article (AJ Speci-cation 07.06) on fire engineering seemed clear to us and to others. It contained the following phrases:
'during the design process, the structural engineer tends to overlook the inherent fire resistance of the steel structure';
'in most cases, structural elements will have a percentage of inherent fire resistance which is not often taken into account'; and 'fire protection to steel is normally specified using the Association for Specialist Fire Protection (ASFP) fiYellow Bookfl which does not consider the performance of a structure in a fire. This results in over provision of fire resistance'.
Our attention was drawn to this article by ASFP members because their good advice and integrity is being pushed aside in favour of a 'double accounting' procedure, as seemingly advocated in the second quote above. To our mind, and also to some site engineers and architects, the article suggests that the period of fire resistance as required by Approved Document B, Fire Safety, say 90 minutes, can be reduced to 60 minutes if the steel has an inherent fire resistance of, say, 30 minutes, and that the thickness of fire protection can be reduced to that required for 60 minutes.
This procedure is not viable, because:all the listed thicknesses of fire protection systems for steelwork, boards/sprays/intumescent paint/epoxy coatings, already include the inherent fire resistance of the steel element at stated critical temperatures. The ASFP is well aware that lower protection thicknesses will exist for other higher critical temperatures. This approach isn't new and doesn't reduce the fire design periods or the potential exposure temperatures associated with the design period;
the algebraic subtraction of one fire resistance period from another is not acceptable practice. The temperatures associated with the original exposure period (90 minutes in the example) will still apply to the rest of the building and to other provisions associated with the steelwork; and interestingly, in correspondence leading up to this letter, Mr Bernabé's company has now suggested - by example - the potential for redundant load-carrying capacity in long-span beams as another opportunity to reduce fire-protection levels in buildings.
This is interesting, since ASFP members are closely associated with steel suppliers and researchers in examining the fire-protection requirements for certain forms of long-span beams, and also for any specialist fire protection measures that may become necessary.
Comment will be added to the ASFP publication 'Fire protection for structural steel in buildings' - the 'Yellow Book' - in due course.
The ASFP Yellow Book already includes the inherent fire resistance of steelwork in every protection system thickness as listed.
The ASFP and AJ Specification has a duty of care to request Mr Bernabé to remove/retract any form of 'double accounting' from the article, whether intended or not, for the fire safety benefit of all.
In other industries, 'product recall' would probably need urgent consideration.
Bill Parlor, technical officer, Association for Specialist Fire Protection