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13 NACE INTERNATIONAL: VOL. 55, NO. 12 MATERIALS PERFORMANCE DECEMBER 2016 requires intumescent f ireproof ing, and that you give these to a coating supplier and they tell you at what dry f ilm thick- ness (DFT) the materials need to be applied to achieve a certain f ire rating. I was reviewing some literature lately, and I was surprised how some companies indicate just 50 mils DFT across the board on every thing and this just seemed to knock my common sense and experi- ence around a bit. A: An arbitrary thickness is wrong as these are supposed to be related to fire-tested assemblies in accor- dance with ASTM E119 testing that is directly related to duration durability during a defined time frame (e.g., 1 or 2 h, etc.). e calculations of the steel assem- bly also must take into account the wet/ dry measurements, so this is what fire protection engineers focus upon. I have seen many intumescent coatings that have disbonded and will not perform in a f ire condition. If their swell- ing cannot be activated effectively, they will not protect the steel as they are not attached. They are no longer insulating the steel that can lose half its structural strength at 700 °F (371 °C). Thus, the insurance issues and the liability about this life safety issue are key, not to mention other considerations. A: I recommend referring to Table 2.3 in ACI 216.1-97/TMS 0216.1- 97, "Standard Method for Determining Fire Resistance of Concrete and Masonry, Construction Assemblies." A: You are correct in saying that the DFT of intumescent coatings required to achieve a particular fire rating depends on the structural steel's section factor, which varies from steel member to member, and needs to be calculated for each. Having said all of that, when you look at loading tables for intumescent coatings, you may find that the specified DFT for a 30-min fire rating is almost unchanged throughout the table, the simple reason for that being it's the minimum and it's suffi- cient for large and small pieces. As soon as you move to 60- and 90-min ratings though, you will see the DFT requirement changing over a wide range. To take your example of 50 mils DFT, that doesn't sound like a 30-min job, and so to have it uniform on all members is not right, the caveat being, of course, that the steel members on that project coinci- dentally have the same section factor and require the same thickness. MP Buyers Guide Online The MP Buyers Guide is an exclusive directory of manufacturers, suppliers, and consultants worldwide that provide products and services for the prevention and control of corrosion. To access the online version of the MP Buyers Guide, as well as add or edit your company's listing, please go to mpbuyersguide.com.