Earthquakes rarely cause fires directly, but the ground shaking creates the conditions for secondary ignitions that can be devastating. These post-earthquake fires, sometimes called conflagrations, are a significant secondary hazard, often causing more widespread destruction than the initial seismic event itself. The movement of the earth damages the complex infrastructure of modern cities, releasing flammable materials and simultaneously introducing ignition sources. This combination of newly available fuel and sparks, coupled with impaired fire suppression capabilities due to damaged water systems and blocked roads, allows fires to spread rapidly and become uncontrollable in urban environments.
Ignition from Damaged Gas Lines
Ruptured natural gas infrastructure historically serves as the leading cause of massive post-earthquake fires in urban areas. Intense ground shaking and soil deformation rupture underground transmission pipes, distribution lines, and smaller service lines leading into buildings. The escaping gas, primarily methane, mixes with oxygen in the surrounding air, creating a highly flammable mixture.
The ignition source may be a pilot light still burning on a gas appliance, an electrical short from a damaged wire, or a spark generated by the fracturing or friction of the pipe itself. Once ignited, the continuous supply of gas from the pressurized network provides an unending fuel source, making extinguishing the resulting fires incredibly difficult.
Damage often occurs where service lines connect to buildings or where unanchored appliances, such as water heaters or furnaces, are violently tipped over. Even within a building, the movement can shear the lines connecting to stoves or dryers. Earthquake-actuated shutoff valves are a modern mitigation measure designed to halt the flow of gas immediately after strong shaking is detected, preventing this continuous fuel supply.
Electrical System Failures
Electrical system failures provide a second major source of ignition following seismic activity. The damage occurs in both external and internal electrical networks, creating arcs and shorts capable of igniting nearby combustible materials.
External failures involve the collapse of utility poles or the severe swaying of overhead power lines, causing them to contact one another or fall onto metal objects, resulting in electrical arcing. Damaged transformers can also short-circuit and explode, scattering burning materials. The risk is compounded by delayed ignition, where power is restored to a damaged system, causing a short circuit in a previously de-energized line.
Internal electrical failures result from structural damage within buildings, where the frame shifts and tears wiring inside walls. This fraying or severing of conductors leads to a short circuit, creating sparks inside the wall cavity or near flammable insulation. Appliances that are dislodged or overturned during the shaking can also sustain internal damage, causing electrical shorts.
Industrial Fuel and Chemical Spills
Earthquakes also pose a specialized, high-volume fire hazard by rupturing large industrial storage facilities. Industrial tanks holding petrochemicals, such as gasoline, diesel, or crude oil, are vulnerable to collapse or rupture from ground motion and soil liquefaction. This releases massive quantities of highly ignitable liquid fuels into the environment, where they can form pools or vapors.
These spills can be ignited by any nearby spark, including those from electrical failures or friction from moving debris. Fires at port facilities or refineries, where large fuel depots are common, can burn for days and release toxic combustion products into the air. “Liquid sloshing” in partially full tanks can compromise the structural integrity of the tank shell, leading to failure and catastrophic release of flammable contents.
Chemical plants present an additional danger, as the rupture of smaller storage drums and containers can lead to the mixing of reactive materials. This unauthorized mixing may cause exothermic reactions that result in spontaneous combustion or the release of volatile, ignitable vapors. The specialized nature of these industrial materials requires unique suppression strategies that are often severely hampered by the seismic damage that caused the spill.