A cautionary note to pass along to employees who weld outdoors: Hot weather can add to the risk of an explosion.

An explosion that killed two welders was caused by flammable fumes inside an aboveground storage tank.

On July 23, an explosion at a natural gas well near Pittsburgh, PA, owned by Huntley & Huntley, killed two workers who were hired to repair pinhole leaks in the oil tank. The two welders worked for Northeast Energy Management of Indiana, PA.

The 8,400 gallon-capacity tank had only about 200 gallons of oil in it at the time.

The Allegheny County Fire Marshal says on the day of the explosion, temperatures were in the 90s with a heat index near 100. The metal tank heated up, causing oil vapor to fill it. The welders were killed when a spark ignited that vapor, causing the five-ton tank to rocket above 100-foot-tall trees and land about 220 feet away.

OSHA is also investigating the explosion.

Huntley & Huntley has no previous OSHA violations. Northeast Energy Management paid $5,965 to settle seven violations after a September 2007 explosion and fire at another well in Pennsylvania. OSHA said workers at that well “were exposed to an unsafe air mixture environment resulting in an explosion and fire causing injuries.”

OSHA’s web page on welding hazards is here.

Tags: 2 workers killed, explosion, oil vapors