What is in this article?:
- Dust plus ignition can be deadly; cotton gins wrongly accused
- Test procedure flawed
- It’s not just the dust that’s trouble in grain bin explosions.
- Without an ignition source an explosion or “deflagration” is highly unlikely.
- Tests show that 87 percent of the dust in a cotton gin does not burn.
CALVIN PARNELL, Texas A&M Regents Professor and cotton chair in the biological and agricultural engineering department and director of the Center for Agricultural Air Quality Engineering and Science, discusses cotton gin and grain bin dust explosions at the recent Coastal Bend Grain storage and handlers Safety conference in Sinton.
Test procedure flawed
“We found the test procedure was not correct. (Other labs) were using pressure only to determine explosibility.”
If pressure increased in an enclosed container to more than 1 bar (about 14.5 psi) they considered the tested dust explosible. “We found that the ignition alone, using 10,000 joules, would create 1 bar of pressure,” Parnell said. “We could get the same reading with no dust in the chamber.
“We see flaws in the procedure (OHSA is using). So we developed a new one. We focus on the inerts in the dust. There is a lot of ash content, for instance, that prevents a deflagration in the chamber. There is not enough MEC, and we couldn’t get results at any concentration.
“We feel like we have a more correct procedure instead of relying on pressure only. Our tests show that 87 percent of the dust in a cotton gin does not burn. OSHA is using results from an incorrect testing system,” he said. “They will have gin dust classified as explosible when it’s not. They err on the side of safety but we can do better than that. It takes time to make changes (in regulations),” he said. “But we need to make changes.
“We also need to find ways to prevent dust explosions and keep people from getting hurt. We are more likely to see MEC in grain bins. We cannot control MEC, so we have to make certain we have no ignition sources.” Those may include faulty wiring, hot bearings or cigarettes or cigars. “Insist on ‘no smoking’ when loading or unloading grain,” Parnell said.
Primary explosions typically begin in the boot or leg of unloading equipment. “We must eliminate ignition sources, especially at grain transfer points where MEC are most likely. That’s where we find primary explosions followed by multiple secondary explosions that can move tons of concrete outside a building. That’s a very serious issue.”