OSHA’s Grain Handling Standard 29 CFR Part 1910.272 addresses grain dust explosion prevention and includes requirements for written housekeeping programs to address grain dust accumulations.
One of the goals OSHA’s housekeeping requirements is to reduce the potential for secondary explosions.
Why are secondary explosions so powerful?
Secondary explosions occur when the blast or pressure wave from the primary explosion propagates into areas such as gallery floors, tunnels, and intermediate floors of the headhouse causing layers of dust to become suspended.
The pressure wave travels away from the primary explosion at approximately 1,000 feet per second followed by the flame wave at 10-100 feet per second.
The pressure wave places dust into suspension, and the slower flame wave ignites these concentrations resulting in powerful secondary explosions.
Primary explosions generate pressures around 2 psi, while secondary explosions can generate pressures in excess of 100 psi.
The rupture strength of equipment, such as bucket elevator legs and conveyors, is around 2 psi while the rupture strength for concrete is roughly 25 psi.
What can you do to prevent secondary explosions?
Follow the requirements of your company’s written housekeeping program to include routine inspections and cleaning of priority areas. Priority areas are defined as floors within 35 feet of an inside bucket elevators and floors of enclosed areas containing grinding equipment.
Remove dust accumulations at priority areas using an action level of 1/8 inch (.32 cm) of accumulated dust.
Clean dust accumulations from motors, critical bearings, and other ignition sources in the work area such as bucket elevators, milling machinery, and similar equipment.
Focus cleaning efforts on hard-to-reach surfaces of equipment, spouting, ledges, and walls.
Can I use compressed air to clean?
Using compressed air for cleaning is acceptable but does pose significant risk since these efforts place dust into suspension. For this reason, OSHA requires that the use of compressed air to blow dust from ledges, walls, and other areas only be permitted when:
All machinery that presents an ignition source is shut down
All other known potential ignition sources in the area are removed or controlled.
Safety doesn’t have to be difficult. Simple steps, like focusing housekeeping efforts on priority areas, can prevent secondary explosions.
