Tire fires resulting from equipment operation are not the only causes of rare but potentially deadly off-road tire explosions. Improper maintenance activities have also caused explosions.

In 1998, a maintenance worker was killed and two coworkers seriously injured at a limestone quarry in Texas. According to the Mine Safety and Health Administration's investigation report, the workers placed a scraper tire flat on the ground in order to remove the brake drum from the rim. Following unsuccessful attempts to hammer and pry off the brake drum, maintenance workers decided to split it. Using an oxygen/acetylene torch, a welder cut 1-in. slots on opposite sides of the cast iron drum.

After a lunch break, the maintenance workers used a water hose to cool the drum and then used a pry bar inserted into one of the cut slots to try to remove it. The drum moved slightly and then the tire exploded.

The explosion turned the tire inside out and sent pieces of the side wall in all directions. In addition to the fatality and injuries, adjacent buildings and a maintenance truck were damaged. The force of the blast was detected as far as a half mile away, MSHA said.

"Use of the torch to cut the brake drum transferred sufficient heat to ignite material within the tire, generating combustible vapors and increased pressure," MSHA concluded. "Heat from the burning material ignited the combustible vapors within the tire, causing it to explode."

MSHA recommends: * never applying a heat source to a tire rim/hub until the tire is removed from rim/hub assembly;

* consulting and following the manufacturer's guidelines for tire and brake drum removal; and

* providing tire and rim safety training to maintenance personnel who service tires and rims.