702 Incident and Accident Investigation

The Hierarchy of Control (HOC) Strategies

The Hierarchy of Controls (HOC) provides a systematic way to select controls for workplace hazards. Control strategies are ranked according to how effectively they can protect workers.

In general, controls that eliminate or control a hazard at its source are preferred over controls that depend primarily on worker behavior or personal protective equipment (PPE).

When developing incident investigation recommendations, use the hierarchy to consider the most effective and practical ways to eliminate or control the hazards identified during the investigation.

HOC Higher Priority Strategies

The HOC gives priority to eliminating hazards or controlling them at their source. Investigators should first consider elimination, substitution, and engineering controls when developing recommendations. These controls generally provide more reliable protection because they depend less on individual worker actions.

1. Elimination: Physically remove the hazard so it no longer exists. Examples include eliminating an unnecessary hazardous process or performing work at ground level instead of at height.
2. Substitution: Replace a hazard with a less hazardous material, process, or method. For example, replace a toxic chemical with a less hazardous alternative.
3. Engineering controls: Isolate workers from the hazard or reduce exposure through physical design or modification. Examples include machine guards, local exhaust ventilation, enclosures, and guardrail systems.

HOC Lower Priority Strategies

Warning system controls, administrative controls and the use of PPE generally rank below elimination, substitution, and engineering controls because they do not eliminate or mitigate the hazard itself at its source, and they depend heavily on employees consistently following established safety requirements.

4. Warning System Controls: Warning systems may be dynamic or static. Dynamic warning systems include visual, audible, voice, and tactile alarms and sensors that alert workers when a hazardous condition exists. Static warning systems include signs and labels that communicate information about workplace hazards. Some warning systems may be integrated into equipment or engineering systems, while signs, labels, cones, and other warning methods function as administrative controls. A worker responding to a warning may avoid or reduce exposure, but that response doesn't eliminate the hazard itself.
• Note: This course lists warning systems as a separate level of the HOC consistent with the ANSI Z10 standard. OSHA, however, generally includes warnings as administrative controls.
5. Administrative/Work Practice Controls: These controls change how work is organized or performed to reduce exposure. Examples include safe work procedures, restricted access, job rotation, work/rest schedules, and training.
6. Personal Protective Equipment (PPE): Provides a barrier between workers and hazards. Examples include gloves, safety glasses, respirators, and hearing protection. PPE does not eliminate the hazard and may need to be used with other controls when higher-level controls do not provide adequate protection.

Use Multiple Controls When Needed

A single control may not provide adequate protection. Investigators should consider using a combination of controls when necessary. For example, an engineering control may also require inspection, maintenance, employee training, and PPE to ensure workers are adequately protected.

Higher-level controls should be considered first, but effective solutions may require the use of several levels of the HOC together. OSHA explicitly recommends combining control options when one method does not fully protect workers. It also recommends worker input when evaluating whether controls will be feasible and effective.

Interim Measures

Using a lower-priority HOC method over a higher-priority control strategy may be appropriate for providing temporary protection until the hazard is permanently abated. OSHA expects employers to protect workers from recognized serious hazards without delay and to use interim controls while permanent solutions are put in place; those interim measures should not become a substitute for feasible higher-level controls.

For more information on the HOC, see OSHA's publication Identifying Hazard Control Options: The Hierarchy of Controls.

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