Fire Investigation

[SteelPE]

I have been asked by a client to visit on of their buildings where a fire recently broke out. This visit is scheduled for tomorrow morning.

From what I can gather the existing structure was used as a wood shop. A spark ignited some sawdust causing the fire. I have not visited the structure yet, but I am under the impression that the building was constructed in the late 60's and consists of unprotected steel joists supporting some form of deck.

I have some experience in dealing with these types of problems. I know how steel performs under varying temperatures, decreased Fy and E, with total loss occurring around 1200-1300F . I know the larger the member the longer it takes the steel to reach the ambient air temp (something that doesn't bode well for steel joists).

When I go out onsite, I am going to basically be looking for any permanent deflection that may have been caused by the fire. If given access, I may even try to see if I can find any welds that maybe compromised. Anything else I should be aware of?

 

[Ron]

Look closely at the welds and even take a pry bar with you to insert between the angles and give a tug. Cracked welds are common, depending on how the fire was extinguished. Sometimes they dump so much water on there the steel is essentially quenched. Big temp swings will crack those small OWSJ welds.

 

[msquared48]

Oh... And I would advise that you stand to the side when you pry on the bar.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[SteelPE]

I am being asked to come up with a plans for a new roof over the area rather than assess the condition of the roof (so it is slightly different but similar). I may be able to make some safe generalizations.

I have been emailed pictures and you can see some areas where the soot is black and others where the soot is white. From what I understand white soot means the fire was burning extremely hot. You can see in the pictures where the joists were sagging due to the extreme temp. It's kind of amazing that they roof didn't collapse. It appears as if most of the damage is localized around a dust collection unit which I think caught fire.

Will find out more tomorrow.