Confined Space Entry...Recognizing and Controlling Hazards

The following article is based on a presentation at a two-day Great Plains Regional Conference sponsored by four Grain Elevator and Processing Society (GEAPS) chapters.

The conference was held in August on the Kansas State University campus at Manhattan. Hans McDonald, compliance officer for Archer Daniels Midland Co.�s Collingwood Grain Division in Hutchsion, KS (620-663-7121), gave the presentation.

On average, five people are killed and additional people are injured every year inside commercial grain storage structures, according to Occupational Safety and Health Administration (OSHA/www.osha.gov) statistics.

All of these injuries and deaths are preventable. The key to safe entry into grain storage tanks is recognizing and controlling hazards that may be present.

OSHA regulates grain storage structure at grain elevators, feed mills, flour mills, rice mills, dust pelletizing mills, dry corn processing plants, and soybean processing plants under 29CFR 1910.272(g). (The complete text of the standard is available on OSHA�s web site.)

OSHA�s grain storage structure entry standard is performance-based, that is, there are specific procedures employers must follow when an employee enters a grain storage structure.

The employer must keep a record of these procedures, and these records must be fully accessible to OSHA inspectors.

Potential Hazards

A variety of hazards must be considered before an employee enters a stored grain structure.

Atmospheric hazards. Oxygen levels must be measured prior to entering a grain storage structure.

Oxygen levels may decrease inside a grain storage structure as grain undergoes respiration, a process that produces carbon dioxide.

The acceptable oxygen level range for safe grain storage structure entry is 19.5% to 23.5%. A worker�s judgment quickly becomes impaired below 16%, and death will occur when oxygen concentrations drop below 6%.

The presence of toxic gas is another potential hazard. The most common gases that could be present in a grain storage tank include fumigants such as phosphine and carbon monoxide...OSHA has set toxic ceiling limits of 0.3 ppm for phosphine and 35 ppm for carbon monoxide.

Entrants must exit the grain storage structure immediately when toxicity concentrations exceed these levels.

Easy-to-use monitors are available for testing oxygen, phosphine, and carbon monoxide concentrations.

The user should be aware of the accuracy limitations of these instruments. Most importantly, these instruments should be bump tested prior to each use and fuly calibrated monthly using test gas of known concentrations.

Finally, flammable gases are a potential hazard. Natural gas and methane may be found in a grain storage structure, if there were some type of gas leak in the area.

For this reason, the grain storage structure should be checked for the presence of flammable gases and vapors prior to entry.

For safe entry, flammable gase or vapor levels must be 10% or less of the lower explosive limit.

Mechanical hazards. Any grain handling equipment associated with a confined space is a potential hazard to entrants, if the equipment unexpectedly energizes during entry procedures.

This includes tank filling equipment such as legs, conveyors, distributors, spouts, and gates, and tank unloading equipment such as augers, belt conveyors, paddle conveyors, and en masse conveyors.

All of this equipment must be shut down properly, isolated, de-energized, locked out, and tagged prior to entry.

Sweep augers can be particularly hazardous to workers inside a grain storage structure.

A good rule of thumb is to stay at least three feet away from a sweep auger.

Never walk on the feed side of the auger, unless it has been locked out and tagged properly.

Some grain handlers attempt to eliminate potential hazards related to sweep augers simply by not using this approach to empty their grain storage structures.

They install doors in the sidewall of the grain storage structure to allow a worker on a skid-steer loader to enter the tank and fully complete the cleanout process.

Before doing so, however, elevator managers should make sure that sturdy grates are covering all floor openings, so the skid-steer loader will be safely supported when passing over these floor openings.

Automated aeration/unloading systems such as PM Luft Inc.�s Kanal System eliminates the need for workers to enter a grain storage structure, until final dettailed cleaning operations are required.

Engulfment hazards. Whenever loose material such as grain is piled up, an engulfment hazard has been created. A few guidelines for dealing with these hazards:

� Never �walk down� grain under any circumstances.

� Wherever an engulfment hazard is present, a worker entering the grain storage structure must be equipped with a body harness and lifeline or a boatswain�s chair to prevent the entrant from sinking further than waist-deep in the grain.

� Bridged grain, a hollow space formed beneath the surface of seemingly-solid grain, is a particularly dangerous situation. If you cannot fully demonstate that the entire grain mass is solid, then you must assume that it is bridge and follow all engulfment prevention procedures.

Written by Ed Zdrojewski, editor

• OSHA