Hierarchy of hazard controls. Hierarchy of hazard control is a system used in industry to prioritize possible interventions to minimize or eliminate exposure to hazards. It is a widely accepted system promoted by numerous safety organizations. This concept is taught to managers in industry, to be promoted as standard practice in the workplace. It has also been used to inform public policy, in fields such as road safety. Various illustrations are used to depict this system, most commonly a triangle.

The hazard controls in the hierarchy are, in order of decreasing priority:
 Elimination
 Substitution
 Engineering controls
 Administrative controls
 Personal protective equipment
The system is not based on evidence of effectiveness; rather, it relies on whether the elimination of hazards is possible. Eliminating hazards allows workers to be free from the need to recognize and protect themselves against these dangers. Substitution is given lower priority than elimination because substitutes may also present hazards. Engineering controls depend on a well-functioning system and human behaviour, while administrative controls and personal protective equipment are inherently reliant on human actions, making them less reliable.

History 

During the 1990s TB outbreak, resulting from the HIV epidemic in the United States, the hierarchy of controls was described as a way for healthcare workers to mitigate their exposure to TB. The hierarchy can be summarized, from most to least preferable, as the following list states:
 "Substitution": Avoids the hazard, which is not possible in a healthcare setting.
 "Contain [the hazards] at their source": Using administrative controls, screen for a given health hazard (in this case, TB).
 This can include source control, which can involve masking an infected patient.
 "Engineering controls": This usually involves configuring isolation rooms and HVAC systems to prevent the spread of infection.
 "Establish barriers": Personal protective equipment, with respirators.

Today's hierarchy has several differences, however keeping the original idea.

Components of the hierarchy

Elimination

Physical removal of the hazard is the most effective hazard control. For example, if employees must work high above the ground, the hazard can be eliminated by moving the piece they are working on to ground level to eliminate the need to work at heights. However, often elimination of the hazard is not possible because the task explicitly involves handling a hazardous agent. For example, construction professionals cannot remove the danger of asbestos when handling the hazardous agent is the core of the task.

The most effective control measure is eliminating the hazard and its associated risks entirely. The simplest way to do this is by not introducing the hazard in the first place. For instance, the risk of falling from a height can be eliminated by performing the task at ground level. Eliminating hazards is often more cost-effective and feasible during the design or planning phase of a product, process, or workplace. At this stage, there’s greater flexibility to design out hazards or incorporate risk controls that align with the intended function. Employers can also eliminate hazards by completely removing them—such as clearing trip hazards or disposing of hazardous chemicals, thus eliminating the risks they pose. If eliminating a hazard compromises the ability to produce the product or deliver the service, it's crucial to eliminate as many risks associated with the hazard as possible.

Substitution

Substitution, the second most effective hazard control, involves replacing something that produces a hazard with something that does not produce a hazard or produces a lesser hazard. However, to be an effective control, the new product must not produce unintended consequences. For example, if a product can be purchased with a larger particle size, the smaller product may effectively be substituted with the larger product due to airborne dust having the possibility of being hazardous.

Eliminating hazards and substituting safer alternatives can be challenging to implement within existing processes. These strategies are most effective when applied during the design or development phases of a workplace, tool, or procedure. At this stage, they often represent the most straightforward and cost-effective solutions. Additionally, they present a valuable opportunity when selecting new equipment or methods. The Prevention through Design approach emphasizes integrating safety considerations into the design of work tools, operations, and environments to enhance overall safety and efficiency.

Engineering controls
The third most effective means of controlling hazards is engineered controls.  These do not eliminate hazards, but rather isolate people from hazards.  Capital costs of engineered controls tend to be higher than less effective controls in the hierarchy, however they may reduce future costs. A main part of engineering controls, "enclosure and isolation," creates a physical barrier between personnel and hazards, such as using remotely controlled equipment. As an example, fume hoods can remove airborne contaminants as a means of engineered control.

Effective engineering controls are integral to the original equipment design and work to eliminate or block hazards at the source before they reach workers. They are designed to prevent users from modifying or tampering with the controls and require minimal action from users to function effectively. These controls operate seamlessly without disrupting the workflow or complicating tasks. While they may have higher initial costs compared to administrative controls or personal protective equipment (PPE), they often result in lower long-term operating expenses, especially when safeguarding multiple workers and potentially saving costs in other operational areas.

Administrative controls

Administrative controls are changes to the way people work. Examples of administrative controls include procedure changes, employee training, and installation of signs and warning labels, such as those in the Workplace Hazardous Materials Information System.  Administrative controls do not remove hazards, but limit or prevent people's exposure to the hazards, such as completing road construction at night when fewer people are driving.

Administrative controls are ranked lower than elimination, substitution, and engineering controls because they do not directly remove or reduce workplace hazards. Instead, they manage workers' exposure by setting rules like limiting work times in contaminated areas. However, these measures have limitations since they don't address the hazard itself. Where possible, administrative controls should be combined with other control measures.

Examples of administrative controls include:

 Implementing job rotation or work-rest schedules to limit individual exposure.
 Establishing a preventive maintenance program to ensure equipment is functioning properly.
 Scheduling high-exposure tasks during off-peak times when fewer workers are present.
 Restricting access to hazardous areas.
 Assigning tasks only to qualified personnel.
 Posting warning signs to alert workers of potential hazards.

Personal protective equipment

Personal protective equipment (PPE) includes gloves, Nomex clothing, overalls, Tyvek suits, respirators, hard hats, safety glasses, high-visibility clothing, and safety footwear.  PPE is often the most important means of controlling hazards in fields such as health care and asbestos removal. However, considerable efforts are needed to use PPE effectively, such as training in donning and doffing or testing the equipment.  Additionally, some PPE, such as respirators, increase physiological effort to complete a task and, therefore, may require medical examinations to ensure workers can use the PPE without risking their health.

Employers should not depend solely on personal protective equipment (PPE) to manage hazards when more effective controls are available. While PPE can be beneficial, its effectiveness relies on correct and consistent use, and it may incur significant costs over time, especially when used daily for multiple workers. Employers must provide PPE when other control measures are still being developed or cannot adequately reduce hazardous exposure to safe levels. Personal Protective Equipment (PPE) minimizes risks to health and safety when worn correctly, including items like earplugs, goggles, respirators, and gloves. However, PPE and administrative controls don't eliminate hazards at their source, relying instead on human behavior and supervision. As a result, they are among the least effective methods for risk reduction when used alone.

Role in prevention through design 
The hierarchy of controls is a core component of Prevention through Design, the concept of applying methods to minimize occupational hazards early in the design process. Prevention through Design emphasizes addressing hazards at the top of the hierarchy of controls (mainly through elimination and substitution) at the earliest stages of project development.

NIOSH’s Prevention through Design Initiative comprises “all of the efforts to anticipate and design out hazards to workers in facilities, work methods and operations, processes, equipment, tools, products, new technologies, and the organization of work.”

Variations on the NIOSH control hierarchy 
While the control hierarchy shown above is traditionally used in the United States and Canada, other countries or entities may use a slightly different structure. In particular, some add isolation above engineering controls instead of combining the two. The variation of the hierarchy used in the ARECC decision-making framework and process for industrial hygiene (IH) includes modification of the material or procedure to reduce hazards or exposures (sometimes considered a subset of the hazard substitution option but explicitly considered there to mean that the efficacy of the modification for the situation at hand must be confirmed by the user). The ARECC version of the hierarchy also includes warnings as a distinct element to clarify the nature of the warning. In other systems, warnings are sometimes considered part of engineering controls and sometimes part of administrative controls.

Use of hierarchical controls 
The hierarchy of controls serves as a valuable tool for safety professionals to determine the most effective methods for managing specific hazards. By following this hierarchy, employers can ensure they are implementing the best measures to protect their employees from potential risks.

When encountering a hazard in the workplace, the hierarchy of hazard control provides a systematic approach to identify the most appropriate actions for controlling or eliminating that hazard. Additionally, it aids in developing a comprehensive hazard control plan for implementing the chosen measures effectively in the workplace.

It is important to be aware of the following when using the hierarchy of controls:

 Use interim controls: If more time is needed to implement long-term solutions, the hierarchy of controls should be used from the top down as interim controls in the meantime.
 Avoid introducing new hazards: Keep in mind is that the selected controls should never directly or indirectly introduce new hazards. Make sure to perform a thorough safety analysis before implementing the selected controls.
 Use a combination of controls: If there is no single method that will fully protect workers, then a combination of controls should be used.

See also
 ARECC - Decision-making framework and process used in the field of industrial hygiene (IH) to anticipate and recognize hazards, evaluate exposures, and control and confirm protection from risks
 
 
 
 
 Normalization of deviance – one reason people stop using effective prevention measures

Notes

References

External links

 Canadian Centre for Occupational Health & Safety document
 Hierarchy of prevention and control measures on OSH Wiki (EU)

Hazard analysis
Occupational safety and health
National Institute for Occupational Safety and Health