Ch. 10 Lightweight steel roof collapse

Question 1

Can steel melt during a fire?

Answer 1

No. Steel requires 2400 degrees F to melt, rarely reached at structural fires.

Question 2

Heated steel expands, bends, twists, sags and buckles when heated by fire. Steel starts to distort and lose strength during a fire when flames reach what temperatures?

Answer 2

1000-1100 degrees F

Question 3

Examples of shaped steel:

general knowledge

Answer 3

• steel bar joist trusses
• steel C beams
• hollow tube steel columns
• steel partition wall studs
• fluted floor decking

Question 4

In the standard time-temperature curve test, fire heated the steel;
1000 degrees F in _____ minutes
1300 degrees F in _____ minutes
fill in the blank

Answer 4

1000 degrees F in 5 minutes

1300 degrees F in 10 minutes

Question 5

Besides the heat of the fire the critical failure temperature of the steel depends on what 3 factors?

Answer 5

• The load it carries
• The dimensions and span of the steel
• The fire protection insulating covering over the steel surface

Question 6

There are 3 common methods of protecting steel from fire, Concrete encasement, membrane ceiling, Spay-on Fire Retarding Material (SFRM). Which one is the least effective?

Answer 6

SFRM is the most popular but least effective.

Concrete encasement offers the greatest protection

Question 7

SFRM fails to protect steel for many reasons, poor or uneven application, slurry not mixed properly, other workers remove to complete their work, or blown off by HVAC system in the plenums. If the steel is not prepared properly to allow the SFRM to stick the application of SFRM over primer paint on steel reduces adhesion of SFRM effectiveness by how much?

Answer 7

1/3 to 1/2

Question 8

Steel heated to 1100 degrees F loses how much of its load carrying capability?

Answer 8

40%

Question 9

What is the danger of concrete encased steel exposed to fire?

Answer 9

Spalling

Question 10

If a fire occurs in an Unoccupied bldg. that has a roof supported by unprotected steel bar joists or C-beams and the stability of the roof is in question, then the roof must be considered too dangerous to send FF’s for ventilation and for an interior hose line. In an Unprotected steel bldg. IC’s should consider a strategy of?

Answer 10

Horizontal ventilation and defensive exterior attack

Question 11

A 50 ft. long steel beam that is heated uniformly over its length from 72 degrees F to 972 degrees F, will increase in length by the average of how much?

Answer 11

3 Feet 9 Inches