Overhead: Live Loads

Article and photos by Gregoy Havel

In the last article, we looked at some of the overhead dead loads that we must be aware of when responding to incidents in addition to the overhead wires we learned about early in our careers. 

In addition to overhead dead loads, we must be concerned with overhead live loads: those that are not permanently attached to or part of the building and that can fall onto us, or that can cause the building to collapse onto us.

 

The most common live loads in a building are people, furniture, merchandise for sale, and stored materials. They are overhead live loads if they are at or near the ceiling, or located on a floor above us.

 

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Photo 1 shows a building containing a retail sales occupancy on the first floor, and several apartments above. If we are inside the first floor, the occupants of the second floor and the contents of their apartments are overhead live loads. If we are on the sidewalk, the overhead live loads include:

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Photo 2 shows drifts of wet, heavy snow that were deposited onto a roof during a Wisconsin blizzard. On either a peaked roof or a flat roof, this amount of live load can exceed the design of the roof structure and weaken it or cause its collapse. On a flat roof with plugged scuppers or roof drains, rain water can accumulate in the same way with similar results. In either case, if there is a fire in the attic or cockloft above the top floor ceiling, the overloaded roof is likely to collapse sooner than we might anticipate. 

Wind and wind gusts are another live load with which we must be concerned. In addition to accelerating the spread of fire inside a building, carrying flaming brands throughout the neighborhood, and providing positive pressure ventilation to a part of the fire building, wind can push against an unstable wall or rooftop structure, impart enough kinetic energy to tip it, and cause an impact load on whoever or whatever is within the collapse zone.

 

Wind can also cause added eccentric load on canopies, awnings, theater marquees, and signboards that extend out from the fronts of buildings, breaking them loose from their connections and causing them to fall.

 

When responding to incidents, we must note the presence of these overhead live loads as a part of our personal and company-officer size-up. The presence of large pieces of furniture and quantities of stored materials on upper floors should also be notes on our preincident plans. Storage issues can also be a housekeeping and life-safety hazard; should be addressed during fire inspections; and should be referred to code enforcement if compliance is not completed.