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Compost Safety: Know Your Confined Spaces
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Compost Safety: Know Your Confined Spaces

According to the OSHA standard (29 CFR 1910.147), a confined space, by design, has limited openings for entry and exit; has unfavorable natural ventilation which could contain or produce dangerous air contaminants; is not intended for continuous employee occupancy; and is large enough and so configured that an employee can enter bodily and perform work. The Standard also includes the hazards of engulfment and entrapment.

In a composting facility, risks in confined spaces could include:

  • Compost bins or tanks, more than four feet deep; open or enclosed
  • Engulfment from walking on a pile and sinking into it -- especially if the pile too high for good process control or to avoid compost fires. Even worse, a pile with hot spots could give way under someone as the void space(s) collapse. (A compost engulfment victim shared his story with me!)
  • Entrapment when entering a grinder or mechanical screen and becoming caught.
  • Ventilation housing and ductwork in a compost building.
  • Storm or sanitary sewer, septic tank, utility vault – while these may not be part of the compost process itself, workers need to know about their presence on-site and their hazards, even if the facility forbids entry.

Composting produces gases -- carbon dioxide, ammonia, nitrous oxide, methane, hydrogen sulfide, carbon disulfide. These are  health hazards when they displace air inside composting vessels or enclosed storage bins. Testing the confined space before entry requires an air tester with a direct readout that can check the air for levels of oxygen, explosive gases, and toxic gases.  

The results will indicate the need to ventilate the space before entry using a blower and hose, with the blower kept outside the space in an area of clean air and the hose dropped into the confined space to provide good air overturn. If welding is done in a confined space, welding fumes could collect and increase to hazardous levels. It is also important to inspect welding gas lines to prevent gas lines leaking in the confined space. Gases such as acetylene or oxygen that leak into a confined space could reach explosive levels or lead to a rapid, intense fire. Also, entering any equipment requires locking out that equipment to prevent injury or entrapment from moving parts.

If the test results are not acceptable, mechanical ventilation of the confined space must occur to introduce air and purge the hazardous atmosphere. Then, air monitoring must take place while someone is in the confined space; if an alarm sounds, people exit the space and try to figure out what the problem is and how to correct it before anyone re-enters the confined space.

This post came about as a result of a discussion on the Compost Facility Discussion Group about confined spaces.

Author: Nellie Brown, MS, CIH, is Director of Workplace Health and Safety Programs for the Worker Institute at Cornell University-ILR, providing training and technical assistance on occupational safety and health, including composting. She serves on a Project Work Team for Managing Organic Residuals and authored the chapter “Composting safety and health” in the forthcoming On-Farm Composting Handbook, 2nd Edition. Nellie has presented at several USCC conferences and pre-conference workshops, as well as a Composting Council of Canada Conference and WasteExpo.