Suffocations in grain bins - Minnesota, 1992-1995

Morbidity and Mortality Weekly Report, Oct 4, 1996

Suffocations in grain bins usually occur when bins are being emptied. During emptying, the flowing grain forms an inverted cone with strong enveloping forces, which can quickly draw a person under the surface (Figure 1) (1,2,4-6). A worker walking on stationary grain may sink only 12 inches[paragraph]; in comparison, flowing grain has characteristics of quicksand and can rapidly induce immersion (1,2,4,5). Suffocation also can occur if a worker enters a bin containing caked, frozen, or spoiled grain. When such grain is unloaded from below, an overlying crust forms, which can collapse under the weight of a person standing or walking on the crust (1,2,4-6).

The average annual number of suffocations associated with grain bins in Minnesota increased from 1.3 during 1985-1991 to 2.3 during 1992-1995 (Minnesota Department of Health, unpublished data, 1996). During January-June 1996, three suffocations were reported in Minnesota. This increase may reflect factors such as the increased storage capacities of bins, faster speeds of grain-handling equipment, automation that enables operators to work alone (6), or increased surveillance for agriculture-related deaths.

Measures to prevent suffocations associated with grain bins include 1) updating existing grain bins by installing safety features that are now standard for most newly manufactured bins (e.g., installation of permanent inside ladders and warning stickers to alert workers to the hazards of entrapment and suffocation); 2) installing pressure-sensitive indicators on bin walls to allow workers to determine the level of the grain without entering the bin; 3) using epoxy coatings to prevent caked grain from adhering to the inside walls of bins, and 4) encouraging grain bin manufacturers and distributors to review instruction manuals with customers. In addition, NIOSH recommends the following precautions to reduce the risk for suffocation related to immersion in flowing grain (4,7):

* Workers should be educated about the risks for suffocation and trained in safe work practices and rescue measures applicable to flowing grain hazards.

* Workers should never enter grain storage structures while grain is being loaded or unloaded.

* Workers should never enter storage areas below grain that is adhering to side walls.

* If entry into a bin is necessary, workers should use safety equipment designed to keep the worker above the grain surface; workers should never stand on top of grain. In addition, all conveying equipment, whether automatic or manual, should be shut off, locked, and tagged to prevent inadvertent operation.

* When breaking up surface crusts, workers should remain positioned outside the bin and use a wooden pole or a weighted line to dislodge the crusted grain.

Because workers who enter grain bins also may be exposed to the hazards of confined spaces, grain bins should be identified as confined spaces, and workers should follow established confined space entry procedures when entering bins. Anyone entering a bin should wear a safety harness and a lifeline attached to a fixed external anchor point. In addition, a co-worker should be stationed outside the bin whenever a worker enters. Visual contact and/or audible communication should be maintained between the worker in the bin and the co-worker at all times. When workers enter bins equipped with ventilation fans, the fans should be turned on before entry; when ventilation fans are operating, they can provide airflow through the stored grain and into the bin atmosphere, providing a safer confined-space atmosphere for entry by workers.