Chapter 9 Flat Roof Collapse

Question 1

during the NFPA’s ten year study of firefighters killed by building collapse (56), how many died as a result of roof collapse

Answer 1

19

Question 2

to determine the risk of flat roof collapse, we need to know three facts about any type of roof construction

Answer 2

1. what type of support system
2. what method was used to connect the joist to the supporting walls
3. is there built-up structure above the main roof

Question 3

in the World Trade Center building how long were they steel bar joist

Answer 3

60 feet, unsupported

Question 4

in new and renovated one story and two story commercial structures what are being used as roof support systems?

Answer 4

steel bar joist, which are actually metal truss

Question 5

In fire testing light wood truss can fail within….

Answer 5

5 to 10 minutes

Question 6

what is the most common flat roof supporting member in older ordinary construction buildings

Answer 6

solid wooden joist

Question 7

brick cavity

Answer 7

solid wooden beams are placed within a recess portion of brick wall and cemented into position

Question 8

corbel shelf

Answer 8

wooden joists are not rigidly encased in brick, simply resting on a girder or brick shelf

Question 9

most H type apartment roof joists are resting on

Answer 9

corbel shelves

Question 10

what are some of the dangers that can be encountered when operating on a roof

Answer 10

1. temporary repairs
2. scuttle covers
3. disorientation
4. shafts