Most damage to buildings from ashfall occurs when the load of ash exceeds the strength of either the roof supporting structures or material used to cover the structure sheet metal plywood etc.
How much ash is needed to collapse a roof.
If it rains and the ash becomes wet it becomes much heavier.
4 in 12 in.
One third of building affected experienced collapsed in the mount pinatubo eruption.
Sheet roofs the supporting structure e g.
Triple roof support snow weighs 50 300 kg m 3 but ash is 400 700 kg m 3 or more than double that if saturated with rain.
Rafters or walls or both.
Ash removal efforts significant.
A thick layer of ash can be very heavy the weight may overload roof structures and may lead to the collapse of buildings.
Caution is needed working.
Provided a useful 5 fold classification of roof types for buildings around vesuvio italy and collapse probability functions for five roof typologies under varying ash loads.
Before ash is to be removed ensure that storm water systems are sealed to stop ash entering.
Severe 12 in.
4 0 12 0 in 100 300 mm danger of roof collapse increases damage to trees essential services interrupted.
Remove the swept ash to a suitable dumping site.
This means more than triple the weight of the thickest snow on the roof and there is no telling how much ash will get dumped on the roof.
In addition if an ashfall is accompanied by rain the roof may become slippery and the wet ash could be difficult if.
Most buildings will support the ash load but weaker roof structures may collapse at 100 mm ash thickness particularly if the ash is wet.
Road transport may be halted due to the build up of ash on roads.
About 100 mm of dry ash could collapse a flat roof.
Walking on roofs covered by a layer of ash can be dangerous if there is a thick layer of ash roofs including flat roofs might collapse.
Cars still working may soon stop due to clogging of air filters.
Importantly for the present study seismic and ash fall building vulnerability classes showed a generally poor correlation.
Dry ash has a weight of 400 700 kg m 3 880 1 545 lb yd 3 and rainwater can increase this by 50 100 percent if the ash becomes saturated.
The load associated with an ashfall can cause the collapse of roofing material e g.
A dry layer of ash 4 inches thick weighs 120 to 200 pounds per square yard and wet ash can weigh twice as much.
Damage due to roof loading is dependent on the load from the accumulated ash and the structural strength of the building.
Clearing ash from a roof may prevent collapse but such a decision must be weighed against the risk of personal injury working in a dark ash rich environment people can easily slip from roofs fall from ladders and fall through weak roofs while clearing and removing ash.
The load of ash that different roofs can withstand before collapsing varies greatly flat roofs are more likely to collapse than steeply pitched ones.
1 0 4 0 in 25 4 100 mm weaker roofs can fail at 4 5 inches of compacted wet ash accumulation 40 lb ft2 very heavy.
