Frequently Asked Questions

Fire Protection

I am an architect and want a fire-protection solution that provides a 1-hour rating on a W460x52 edge beam connected to a HSS203x203 column. I can find 4-hour, 3-hour and 2-hour rating values for a combined gypsum board and steel girder assembly but cannot get a 1-hour rating for this manufacturer. What are my alternatives? - R.M.

2/2/2009

It would appear that a common industry practice is to consider three alternatives:

1) Take a higher rating (1.5-hour if it exists for that company, or 2-hour rating).

2) Provide the minimum thickness gypsum board (ignore its contribution) and use another type of fire-protection (cementitious or fibrous) to obtain a 1-hour rating.

3) Use the rating of a column with the beam dimension. Since the column ratings generally include more fire-protection, we can assume this approach to be conservative.

However, before going that route of alternatives, you need to make sure that this assembly does not exist in the ULC directory. Looking at the ULC directory pages under “N” and “O” (beams, floor and ceiling) and the 500 series membrane fire protection with gypsum boards), there are four listings, O501 to O504, all protecting a minimum W200x36 beam with 2 layers of 15.9 mm gypsum board and all having a 2-hour listing. Note though that there might be some listings that were finalized after the annual ULC directory was printed. They might be available from the gypsum board manufacturer directly (one could view their website and get advice from their technical sales staff). But no such luck with your assembly. I know that you have already made your M/D calculations based on NBCC (Appendix D-2.6.4), and took into account a one-layer gypsum board protection but that only yielded a 45-minute rating.

Looking at the three alternatives, the first two alternatives are plausible - one will have to use two layers of gypsum boards (be fire resistant for two hours instead of one) or use 1-hour spray applied fire-resistive material (SFRM, for example 13mm of fibre in N809 gets one hour) and then box in the beam with one layer of thin membrane boards for cosmetics (probably costs more than putting on two layers).

Now for the third alternative. A column isn't a beam — does that sound Shakespearean? By that we mean that the tests are different, i.e. two types of fire tests and gypsum board behaviour — bending beam and unloaded column affect boards differently during the test. Boards can pop off a deflected floor beam assembly close to the end of a test. ULC S101 fire test standard has an unloaded column with its fire protection on it and terminates the test when the temperature of the steel has exceeded 538 deg. C. A beam test on the other hand requires the application of load and three criteria for ending the test - 1) the beam can no longer hold the load; 2) the passage of flame or hot gas is taking place and 3) the temperature limits are in excess of 140 deg. C average or 180 deg. C on the individual thermocouple situated on unexposed side.

I know you have decided on option 3 and you appear not to be alone. Dr. Farid Alfawhakiri of the American Iron and Steel Institute suggests the same approach when you need to get a rating for a HSS beam. Since ratings do not exist for HSS beams, one can conservatively use ratings performed on HSS columns. See the Steel Interchange section in Modern Steel Construction, July 2006 issue.

I would like to thank Louis-Raymond Gratton of A/D Fire and George Frater of the Canadian Steel Construction Council for their help in developing a solution to this question.