Safety Hierarchy and Machine Safety Design Protocol

The consensus safety hierarchy for prevention of agricultural injuries follows five steps, in priority order:

1. Eliminate the hazards, if possible. Observe American Society of Agricultural Engineers (ASAE) and OSHA safety standards.

2. Guard the hazard. Use shield, casing, enclosure, barrier, or interlock.

3. Warn about the hazard.

4. Train the user about the hazard.

5. Protect the user with personal protective equipment.

Often a combination of methods is used. Design engineers have control over the first three steps; therefore, these steps comprise a machine safety design protocol (5).

Eliminating the hazard means using a mechanism that does not include the hazard, if feasible. Guarding the hazard is done when the hazard cannot be eliminated; the hazard may be guarded by a purpose-designed shield or cover, or by location, for example, positioning the hazard in a place inaccessible to the operator. Warning about the hazard is done even for hazards that are guarded if there is any chance that the guard might be removed, but is the primary prevention method where the hazard cannot be guarded. A typical example of the latter is the crop intake of a harvesting machine, where an opening must be provided for the crop to enter the machine. Such an opening might also be used to reach into the machine.

Research has been conducted on presence-sensing devices, such as using infrared or sonic waves, that would shield hazards from personal contact by sensing when a person is present and responding by shutting off the machine. Challenges include prevention of false triggering for mobile machines, shutting off high-inertia machines rapidly, reliability in harsh environments over many years of service, cost, and risk of providing a false sense of security (inviting operators into dangerous areas they would normally avoid because they assume the device will protect them). Because of these challenges, such devices are not currently found on farm machines (6).

Agricultural machine designs evolve, and increasing attention has been paid to safety in recent years, as is true for automobiles. However, unlike automobiles, agricultural machines last for decades, and thus hazards that have been eliminated or guarded in newer machines continue to cause injuries as operators use machines that may be decades old.

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