3.1 Hierarchy of Controls & Safety Engineering Principles
Key Takeaways
- The Hierarchy of Controls ranks hazard mitigation strategies from most effective (Elimination) to least effective (PPE).
- Elimination and Substitution are the most effective because they physically remove or replace the hazard entirely.
- Engineering controls isolate people from the hazard without relying on worker behavior.
- Administrative controls and PPE are considered less effective because they require consistent human action and compliance.
- When implementing controls, safety professionals must consider both technical feasibility and economic viability.
The Hierarchy of Controls: A Foundational Framework
In the field of occupational hygiene and safety, the Hierarchy of Controls is perhaps the most fundamental framework for mitigating workplace hazards. The National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) heavily rely on this system to ensure that the most effective and reliable hazard controls are implemented before resorting to less reliable methods.
The core principle of the hierarchy is that control methods at the top are potentially more effective and protective than those at the bottom. Following this hierarchy normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced.
1. Elimination: The Most Effective Control
Elimination is the process of physically removing the hazard entirely from the workplace. Because it completely eradicates the source of the risk, it is universally recognized as the most effective control method.
Examples of Elimination
- Fall Hazards: Moving a task that was previously performed at heights to ground level. For instance, assembling components on the floor before lifting the entire structure into place completely eliminates the risk of workers falling during the assembly process.
- Chemical Hazards: Completely stopping the use of a dangerous chemical in a manufacturing process and redesigning the process so that no chemical is needed.
- Ergonomic Hazards: Utilizing automated material handling equipment to entirely remove the need for manual lifting of heavy objects.
Challenges
While highly effective, elimination is often the most difficult to implement in an existing process. It usually requires significant design changes and capital investment. Therefore, elimination is most practical and cost-effective when considered during the initial design or development stage of a facility, process, or equipment.
2. Substitution: Replacing the Hazard
Substitution involves replacing something that produces a hazard with something that does not produce a hazard or produces a lesser hazard.
Examples of Substitution
- Toxicity: Replacing a highly toxic solvent, like benzene, with a less toxic alternative, such as a citrus-based cleaner or water-based detergent.
- Physical Hazards: Replacing a high-noise pneumatic tool with a quieter electric alternative, thereby substituting a severe noise hazard with a milder one.
- Fire Risks: Substituting a highly flammable material with one that is non-combustible or has a significantly higher flashpoint.
Considerations
When substituting, safety professionals must carefully evaluate the new material or process to ensure it does not introduce new, unforeseen hazards. For example, replacing a toxic chemical with a less toxic but highly flammable one merely trades one risk for another. The goal is a net reduction in overall risk.
3. Engineering Controls: Isolating the Hazard
If a hazard cannot be eliminated or substituted, the next step is to implement Engineering Controls. These are physical changes to the workplace that isolate workers from the hazard. Crucially, well-designed engineering controls can be highly effective because they generally do not rely on worker behavior or compliance to function properly.
Types of Engineering Controls
| Control Type | Description | Example |
|---|---|---|
| Enclosure | Completely enclosing the hazard to prevent exposure. | Soundproof acoustic enclosures around noisy generators; glove boxes for handling hazardous pathogens. |
| Isolation | Creating a physical barrier between the worker and the hazard. | Machine guards over moving parts; physical barriers separating pedestrian walkways from forklift traffic. |
| Ventilation | Removing airborne contaminants from the work environment. | Local exhaust ventilation (LEV) systems capturing welding fumes directly at the source; general dilution ventilation in a warehouse. |
Design and Cost
Engineering controls often involve a higher initial capital cost than administrative controls or PPE. However, over the long term, operating costs are frequently lower, and they provide a more reliable and consistent level of protection.
4. Administrative Controls: Changing How People Work
Administrative Controls do not remove the hazard; instead, they alter the way work is performed to reduce the duration, frequency, or severity of exposure. Because these controls rely heavily on human behavior, supervision, and ongoing training, they are considered less effective and less reliable than engineering controls.
Examples of Administrative Controls
- Procedural Changes: Developing and enforcing standardized safe work practices (e.g., standard operating procedures for chemical handling).
- Job Rotation: Rotating workers through various tasks to minimize cumulative exposure to repetitive motions, noise, or specific chemicals.
- Scheduling: Scheduling high-hazard tasks, such as heavy maintenance or noisy operations, during off-shifts when fewer workers are present in the facility.
- Training: Providing comprehensive safety training, signage, and warning alarms to alert workers to potential dangers.
5. Personal Protective Equipment (PPE): The Last Line of Defense
Personal Protective Equipment (PPE) is placed at the very bottom of the hierarchy. PPE involves equipment worn by workers to minimize exposure to specific hazards.
Why is PPE the Least Effective?
PPE is considered the least effective control for several critical reasons:
- Reliability: PPE only works if it is selected correctly, fitted properly, worn consistently, and maintained adequately.
- Failure Consequence: If PPE fails (e.g., a respirator seal breaks, or a glove tears), the worker is immediately exposed to the full force of the hazard because the hazard itself has not been eliminated or controlled at the source.
- Comfort and Burden: PPE can be uncomfortable, restrict movement, reduce visibility, and create physiological burdens (like heat stress), which can sometimes lead to reduced compliance or even introduce secondary hazards.
Proper Role of PPE
Despite being the least preferred method, PPE is absolutely necessary in many situations. It is typically used:
- While engineering controls are being installed or evaluated.
- When engineering and administrative controls are not technically or economically feasible.
- During emergency response situations where hazards are unpredictable.
- As a supplementary layer of protection alongside other control methods.
Evaluating Feasibility
When applying the Hierarchy of Controls, OSHA expects employers to implement the highest-level controls that are feasible. Feasibility has two components:
- Technological Feasibility: Can the control be implemented given the current state of technology and engineering?
- Economic Feasibility: Would the cost of implementing the control threaten the financial survival of the business?
Safety professionals must rigorously assess both aspects, often relying on industry consensus standards (like ANSI or NFPA) to determine what is considered feasible and effective within a specific sector.
According to the Hierarchy of Controls, which of the following is considered the most effective method for mitigating a workplace hazard?
Why are administrative controls generally considered less effective than engineering controls?
Which of the following is an example of Substitution?