Before ash is to be removed ensure that storm water systems are sealed to stop ash entering.
How much ash is needed to collapse a roof.
4 0 12 0 in 100 300 mm danger of roof collapse increases damage to trees essential services interrupted.
Ash removal efforts significant.
If possible sweep ash off in a dry state the addition of water will turn the ash into mud which can set like concrete.
1 4 in.
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.
About 100 mm of dry ash could collapse a flat roof.
Be very cautious when working on a roof.
For information on protecting yourself against these hazards visit the following.
A dry layer of ash 4 inches thick weighs 120 to 200 pounds per square yard and wet ash can weigh twice as much.
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.
A common concern during ashfall is the potential collapse of buildings from the weight of accumulated ash on roofs.
Major ash removal operations in urban areas.
After an ashfall buildings that have received more than 100 300 mm 4 12 in of ash and that have not collapsed still run a high risk of load damage including collapse.
One third of building affected experienced collapsed in the mount pinatubo eruption.
The addition of more weight on a roof during cleanup operations can tip the load beyond the structure s load capacity and cause collapse.
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.
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.
When volcanic ash accumulates on buildings its weight can cause roofs to collapse killing and injuring people.
Road transport may be halted due to the build up of ash on roads.
However this is a very rare impact which requires very thick ashfalls typically 100 mm.
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.
Damage due to roof loading is dependent on the load from the accumulated ash and the structural strength of the building.
Severe 12 in.
Ash can be slippery and make it easy to fall.
Remove the swept ash to a suitable dumping site.
Most buildings will support the ash load but weaker roof structures may collapse at 100 mm ash thickness particularly if the ash is wet.
Ash is very heavy and can cause buildings to collapse.
A thick layer of ash can be very heavy the weight may overload roof structures and may lead to the collapse of buildings.
If it rains and the ash becomes wet it becomes much heavier.
Volcanic eruptions may result in floods landslides and mudslides power outages and wildfires.
