The hierarchy of control is a framework for workplace safety that structures protective measures into five distinct categories, organized from most effective to least effective.
Each control in the list presents a general category of activities that a company can undertake to mitigate or even remove hazards from the workplace.
In order of decreasing effectiveness, the five types of control in this hierarchy are:1. Elimination. Physically removing a hazard.
2. Substitution. Replacing a hazard with a lower-risk alternative.
3. Engineering Controls. Separating workers from a hazard.
4. Administrative Controls. Changing the way people work.
5. Personal Protective Equipment. Providing protective equipment like helmets, boots, gloves.
The list of the five controls is generally presented as an inverted triangle, with the least effective method for controlling hazards presented at the bottom, the next least immediately above that, and so on, like this:
The hierarchy of control is a central tenet of workplace safety in companies of all kinds, regardless of the size of the business or the industry that it's a part of.
In fact, government bodies that develop and monitor workplace safety protocols—agencies like OSHA (Occupational Safety and Health Administration) and the CDC (Centers for Disease Control) in the U.S.—consider the hierarchy of control to be one of the very best methods for ensuring worker safety on the job.
By removing hazards through intentional planning, the ultimate goal of using the hierarchy of hazard controls is to help workers avoid work-related illness, injuries, and accidents on site.
Here is menu for this guide in case you'd like to jump around:
- What Is the Hierarchy of Control?
- Hierarchy of Control: The Five Types of Hazard Control
- How to implement the Hierarchy of Control
- Examples of the Hierarchy of Control
- Hazard Controls for Indoor Inspections
- How Drones Fit into the Hierarchy of Control
What Is the Hierarchy of Control?
Though the control and minimization of workplace hazards had long been a topic of discussion, it was the National Safety Council (NSC) that first identified the hierarchy of controls in explicit terms.
The NSC, founded in 1913 and expanded by a congressional charter in 1953, first identified the hierarchy of controls in the 1950s, recognizing that preventative action and elimination of hazards were far more effective in minimizing risk than other “lower level” controls like personal protective equipment, on-the-job training or verbal warnings.
In the seven decades since, safety and regulatory boards across the world have adopted, adapted and further expanded upon the ideas that the NSC originally introduced.
Both the National Institute for Occupational Safety and Health (NIOSH) and OSHA now identify the hierarchy of controls as one of the best methods for minimizing occupational hazards across industries. Both agencies include a number of references to the hierarchy in guides and resources on their respective websites as well.
The National Fire Protection Association (NFPA) has also made the hierarchy a central tenet of best practices for fire and electrical safety. The NSC too, still around to this day, continues to highlight the method and offers a number of articles and guides to the hierarchy on their website.
Hierarchy of Control: The Five Types of Hazard Control
Let's take a closer look at each control in the five types of hazard control.
You can think of each section in the hierarchy of control as a “line of defense” against workplace accidents and occupational hazards.
Though the categories at the top are wider-reaching and more effective, things always slip through the cracks. This is why it's important to implement all parts of the hierarchy in some way, despite their differing rates of efficacy.
At the top of the hierarchy of controls is the elimination of a risk or hazard. This means removing a material or process that poses a risk to workers entirely. Intuitively, this is the most effective category in the hierarchy of controls because if there’s no hazard at all, there’s virtually no risk.
Examples of hazard elimination include:
- Taking equipment placed high above ground and lowering it to the floor before workers repair it.
- Moving machinery that creates a loud noise to its own dedicated room.
- Automating hazardous inspections by using drones or other unmanned vehicles.
Of course, complete elimination of risk isn’t always possible. Sometimes, risk is unavoidable in an industry. Other times, it’s too expensive or work-intensive to completely remove an item or process from an established production line. Retrofitting an entire system with one that is only marginally safer is not viable for many small or medium sized businesses.
It is for this reason then that hazard elimination is best implemented during the planning and design process. This is where prevention through design, as discussed above, comes into play.
When hazard elimination is implemented into the design process, it is often simple and inexpensive. Large changes can still be made, and, while many industries cannot fully eliminate all hazards, addressing risks at the earliest stage possible allows for maximum safety.
Substitution, the second most effective form of hazard control, involves replacing a hazardous material or process with one that poses a lower risk.
Like hazard elimination, hazard substitution is most effective in the design or planning stage of a project, when large, sweeping changes can still be made at a low cost.
Examples of hazard substitution include:
- Replacing a lead-based paint with a safer one like titanium white.
- Using an eco-friendly pesticide in place of one that contains DDT.
- Replacing a piece of cutting equipment with one that has fewer exposed sharp edges.
When implementing hazard substitution controls, businesses must be careful not to produce unintended consequences with their new product of choice. If this occurs—where a process believed to be less hazardous ends producing a new, unexpected risk—it is known as a regrettable substitution.
One well-known example of a regrettable substitution involved a brake cleaner that was phased out due to its dangerous environmental impact. However, its replacement, an organic compound known as hexane, was eventually discovered to be neurotoxic.
3. Engineering Controls
If hazard elimination or substitution is not possible—whether it be because a project is past its development stage or that a safer alternative is just not available—then businesses should turn to the third category in the hierarchy: engineering controls.
Engineering controls attempt to physically separate a human worker from risk. Rather than eliminate a hazard completely, engineering controls aim to isolate people from hazardous processes by placing a barrier between them and the risk at hand.
Examples of engineering controls include:
- Installing guardrails, partitions or sound dampening equipment.
- Reducing the inhalation of toxic material through proper ventilation.
- Using tools, displays and other equipment to create an ergonomically appropriate workplace.
Though engineering controls are not as effective as hazard elimination or hazard substitution, they are still beneficial because they are designed to remove a hazard at its source, before it comes into contact with the worker.
Rather than relying on a worker’s behavior or ability to wear protective equipment, engineering controls physically alter a workplace to make it safer.
Upfront costs of engineering controls tend to be higher than other categories in the hierarchy; however, in the long term, properly instituted engineering controls can not only independently protect workers, but lower operating costs overall. It also saves shareholders money in workplace injury fees and liability insurance.
4. Administrative Controls
The fourth most effective type of hazard control is administrative controls. Administrative controls attempt to change the way that people work by instituting policies, rules, signage or practices that shift workers’ behavior.
While administrative controls do not remove hazards from the workplace, they do attempt to limit a worker’s exposure to any given risk.
Examples of administrative controls include:
- Completing road construction at night when fewer people are driving.
- Requiring employees to wash their hands thoroughly after using the restroom.
- Limiting the amount of hours that drivers of commercial vehicles can be on the road.
Administrative controls are less effective than other types of hazard reduction in the hierarchy because they rely almost fully on human behavior and worker accountability.
Just consider the examples given above; while they do reduce risk, road construction still happens during the day, employees still don’t wash their hands, and truck drivers still drive more hours than they reasonably should. Sometimes, a sign is simply not enough, and it is for this reason that administrative controls are further down the hierarchy.
5. Personal Protective Equipment (PPE)
The final category in the hierarchy of control is personal protective equipment (PPE). This is at the bottom of the hierarchy as it generally is the least effective of all hazard control methods.
Examples of personal protective equipment include:
- Wearing surgical masks to reduce risk or infection.
- Keeping hardhats or steel toed boots on in a construction environment.
- Donning gloves, pads or a hazardous materials suit when handling toxic chemicals.
Personal protective equipment is generally seen as less effective than other hazard control methods because it does not eliminate the hazard and still exposes workers directly to the risk. If either the hazard or the equipment malfunctions or breaks, there is little left standing between the worker and the hazard.
PPE can also burden a worker, rendering them unable to do their job to their best capacity due to uncomfortability or other strains caused by protection equipment. It is for this reason that PPE is typically used as part of a hazard control system and not as the entire process.
Prevention through Design
The hierarchy of controls is part of a wider safety concept known as prevention through design.
Prevention through design (also sometimes known as safety by design in Europe) aims to minimize risk and hazards in the workplace at the top level.
By identifying and “designing out” potential dangers in the planning stages of projects, prevention through design can help stop accidents before they even have a chance to materialize.
Reducing worker risks “at the source” not only minimizes the amount of workplace injuries and deaths, but also helps to maximize returns for all stakeholders. Less injuries means less downtime, which means an increase in both profits and efficiency.
The sections at the top of the hierarchy of control pyramid (namely elimination and substitution) are a key part of preventative safety measures and prevention through design.
In fact, the National Institute for Occupational Safety and Health (NIOSH) considers the process to be “the most effective and reliable type of safety system in preventing occupational harm.”
How to Implement the Hierarchy of Control
Now that we know what the hierarchy of control is and how it’s being used across a number of industries, we can start to examine how to implement it into any given business or workplace.
OSHA has a six-step process on how best to implement the hierarchy of risk control into any business.
The steps to implement the OSHA hierarchy of hazard control are:
Keep reading to learn more about each step.
1. Identify Hazards
Before deciding which part of the hierarchy you need to use to manage a given risk, you, of course, need to identify what the risks in your business actually are.
There are a number of ways to do this. One is through prevention by design, where you “design out” and eliminate any potential hazards in the planning process of a project.
If hazardous materials or processes are already present in your system however, there are a number of ways to identify different potential areas of hazard control. First and foremost, the workers who are and will be exposed to these hazards should be considered and interviewed.
Workers should be asked about their perception of hazards on the job, how they think these hazards could be reduced and whether or not they think that potential solutions and control options would actually be effective.
Once the workers at risk have been consulted, business owners should collect as much data as possible. This includes collecting information about workplace injuries or deaths, examining control measures used in other similar workplaces, and reviewing OSHA guidelines or other regulatory standards.
2. Select Hazards To Control
Once all potential hazards have been identified, business owners should select the risks that will be the most permanent and effective. Important as well is whether or not these control measures would actually be feasible.
Be sure to closely examine the cost associated with each hazard control to see if they are actually viable to your business. Additionally, if there are hazards that are actively causing harm or injury (fires, loose wiring, faulty machinery) take care of those immediately.
From there, it’s time to implement the hierarchy. Try first to identify hazards that you can eliminate or substitute completely, as these are the most effective forms of hazard control. Additionally, be sure to look for equipment and materials that are designed with prevention through design properties in mind. Lastly, make sure that none of your hazard control solutions indirectly introduce new hazards or risks.
3. Make a Hazard Control Plan
Make a plan and stick to it. Whether you’re putting out a fire, instituting interim controls before moving to longer-term solutions or making your way through the hierarchy itself, having a hazard control plan is vital.
Figuring out how you’ll track progress is important as well, as you want to make sure that your hazard control methods are actually working. Determine how you will actually determine success, and establish a date by which you hope to see changes implemented. At minimum, you should report on and update your hazard control plan annually. Plans should also be edited and examined whenever machinery, systems or personnel are swapped or changed.
4. Establish Emergency Controls
While prevention is the goal, emergencies do happen. Depending on your industry, this can be anything from industrial fires to chemical spills to anything and everything in between.
Before you go making preventative changes then, you need to be sure to have systems and processes in place that protect workers during emergencies and non-routine functions.
You can do this by purchasing any equipment needed for emergency operations (fire extinguishers, eye wash stations, etc.) and by running emergency drills regularly.
Additionally, be sure that each worker knows their responsibility in an emergency situation and that emergency services are automatically or promptly contacted when such an emergency occurs.
5. Implement Hazard Controls
You’ve established emergency operations, identified your hazards, selected which hazards to control and determined how you’re going to track these improvements. Now it’s time to actually implement these changes using the hierarchy of control as a guide.
Use a “worst-first” framework, targeting the issues that need to be addressed quickly. From there, begin implementing the changes that will be cheapest and most effective. Regardless of the level of hazard that they involve, these tasks (removal of tripping hazards, basic lighting, and general housekeeping) will have a huge effect on safety and risk management.
6. Confirm That Controls Are Effective
Once you’ve done the above, all that’s left to do is ensure that your new methods of hazard controls are functioning properly.
Are things running according to your established hazard control plan? Are emergency drills being run? Are trends pointing upwards, with fewer workplace accidents?
If so, you should continue tracking results and analyzing the data. From there, you can start all over from the top of the list and continue to maximize safety in your workplace.
Examples of the Hierarchy of Control
Now that we’re familiar with each type of hazard control in the hierarchy, let’s take a look at three examples of how it’s been implemented to reduce risks across a number of industries.
Here's a list of the examples covered in this section in case you'd like to jump around:
According to OSHA, fall protection is the #1 most frequently cited workplace safety violation.
Here’s how the hierarchy of controls has been used in the workplace to minimize the risk of falling on the job.
In this example, hazard elimination would include removing the need for scaffolding or ladders at any given job site.
If that’s not possible, another hazard elimination technique could involve bringing pieces of machinery that are placed high above the ground down to floor level before workers undergo any repairs or maintenance.
If elimination is not possible, businesses could substitute one kind of climbing equipment for another. This would include installing an elevator, switching out temporary ladders for sturdy and fixed ones or changing out flimsy climbing ropes with safer and sturdier ones.
Control 3—Engineering Controls
This would include placing hand and guardrails on site or coating stairs with non-slip material. Any sort of physical improvement that can be made to the workplace without asking workers to change their behavior would be considered an engineering control in this example.
Control 4—Administrative Controls
Administrative controls to limit falling would include only allowing certain employees to work at high elevations, requiring intensive training before allowing workers onto scaffolding, not allowing workers to work at high elevations in low light, and a whole host of other guides and practices aimed at changing worker behavior. Signage that reminds workers of best practices and risks associated with working at high elevations could also be included here.
Control 5—Personal Protective Equipment
Helmets, padded clothing, harnesses, parachutes and personal fall arrest systems are examples of PPE that could be used to help reduce the risk of falling on the job. Since these require the worker’s attention and could also hinder them in doing their job effectively, they are the least effective option.
2. Toxic Materials
Many jobs, such as those in a factory or production line, can expose workers to dangerous, toxic or deadly chemicals or gasses. The hierarchy of control is vital in minimizing the risk that workers face when working in such conditions. Let’s take a quick look at how each control method in the hierarchy can keep workers safe in this situation.
In some situations, like in agricultural industries, the use of a dangerous or toxic chemical could be avoided entirely. If so, this risk should be dealt with through hazard elimination. Since elimination is often most effective during the design and planning process, businesses should determine before starting a project whether or not a certain chemical or particulate is actually necessary in achieving their required outcome. If not, that chemical can (and should) be eliminated from the business plan.
Hazard substitution is often used in industries that deal with toxic materials. In many situations, there is a safer alternative to a number of different chemicals that are used in a product or process. In farming for example, eco-friendly pesticides could be swapped out for ones that harm the earth.
If implementing this level of the hierarchy however, businesses should make sure that their new substitute has no unintended consequences and that the hazard is actually being traded out for a safer option, not just being passed on to another group.
Control 3—Engineering Controls
Instead of eliminating a risk, engineering controls aim to isolate workers from a necessary hazard entirely. In a factory that deals with toxic gasses or materials, this would include proper ventilation and high powered fans to minimize exposure to workers.
Control 4—Administrative Controls
Administrative controls that could limit workers’ exposure to toxic chemicals include shorter shifts, increased staffing, job sharing, training on which materials are most dangerous and other best practices that are taught to workers to alter their behavior.
Control 5—Personal Protective Equipment
In a working environment that deals with toxic materials or gasses, personal protective equipment includes respirators, gloves, hazardous material suits and other protective clothing.
Lastly, let’s take a look at the COVID-19 pandemic.
In addition to being familiar to nearly every human on the globe, there are few better examples of how the hierarchy of risk control can be used to tackle a large, systemic hazard than looking at how the Centers for Disease Control and Prevention (CDC) used the framework to tackle the novel coronavirus pandemic of 2020 and beyond.
The National Institute for Occupational Safety and Health (NIOSH), a subset of the CDC, was a leading proponent of the hierarchy of control model even before the COVID-19 pandemic. NIOSH actually helped to identify and further define many of the categories in the hierarchy today, and it was for this reason that the agency was able to help lead the charge on how to best implement the hierarchy as it related to the coronavirus.
Let’s take a look then at how NIOSH and the CDC used the hierarchy of controls to tackle the all-too-familiar hazard of COVID-19.
In this situation, hazard elimination would be either an all-purpose cure for the disease or a majority of the population inoculated with an effective COVID-19 vaccine..
As we know, substitution involves replacing a hazard with one that poses a lower risk. We cannot (and would not want to) replace COVID-19 with a lower risk disease. However, businesses did replace hazardous, highly-transmissible workplaces with online spaces and remote work.
Control 3—Engineering Controls
Many industries could not go fully virtual, of course. In this case, businesses implemented engineering controls like social distance markings on the floor and plexiglass dividers between workers and customers.
Control 4—Administrative Controls
During the COVID-19 pandemic, administrative controls included mandatory hand washing and the wiping down of high-touch surfaces. Signage that requests that customers social distance themselves or wear masks are also examples.
Control 5—Personal Protection Equipment
PPE became ubiquitous during the COVID-19 pandemic.
Widespread use of masks, gloves and face shields are examples of how this part of the hierarchy of controls was implemented by all during this time.
Hazard Controls for Indoor Inspections
Some types of work do not allow for all five controls to be implemented, at least not when the work is done in a traditional manner.
Indoor inspections are one of these scenarios.
In a traditional internal inspection of a boiler or pressure vessel, the only controls available to site administrators are generally the two lowest levels—PPE and Administrative Controls.
The reason for this is fairly simple.
The three higher tiers of the hierarchy of controls—Engineering Controls, Substitution, and Elimination—all require the hazard to be removed, replaced, or for the person to be isolated from it.
But for indoor inspections that are performed manually, none of these options are available because inspectors must physically enter the confined space in order to perform a visual inspection with their naked eye.
And this fact leaves only the first two levels of control available—unless you can use some kind of robotics solution, like a drone, to completely take the place of the inspector. (We'll cover drones in the next section, which deals with where drones fit into the hierarchy of hazard controls.)
To make the implementation of the hierarchy of controls in an indoor inspection scenario more concrete, let’s take a closer look at examples for those first two levels (PPE and Administrative Controls).
In Oil and Gas, it’s common practice for inspectors and other personnel to use PPE like flame-resistant clothing, steel-toe boots, hard hats, and safety glasses.
And if an inspector is conducting a visual inspection of an asset like an FCC unit, which requires manned entry via rope access, they will also be required to use additional PPE, such as a harness, to keep themselves secure during the visual inspection.
Stepping up one level in the hierarchy of hazard controls, Administrative Controls could be put in place in this instance that would require the inspector’s harness to be systematically checked, or that all FCC unit inspections must follow a certain safety protocol, with a specified administrator or site manager required to sign off on a pre-inspection safety checklist.
These kinds of administrative controls are an improvement on the first step of simply using PPE, since they could help increase the likelihood that workers will use their PPE, as well as increasing awareness about common hazards in FFC unit inspections and how to avoid them.
But this is where the hierarchy of controls ends for manual indoor inspections.
To continue moving up the hierarchy and actually eliminate a hazard, you have to turn to robotics solutions like drones that can completely replace the need for a person to enter a confined space in order to collect visual data on its condition.
How Drones Fit into the Hierarchy of Control
The most effective hazard control in the hierarchy of controls is Elimination—completely getting rid of the hazard to the worker.
But complete elimination of a hazard is a hard thing to accomplish, since it means that you have to completely replace the need for a person to be doing the hazardous task by having it performed some other way.
This is where drones come in.
In indoor inspection work, drones can completely eliminate the need for a person to enter a confined space, allowing inspectors, administrators, and project managers to completely eliminate the need for a person to place themselves in a hazardous situation.
[Related reading: Can a Drone Be Used as a Formal Inspection Tool?]
For example, for an API 510 Pressure Vessel Inspection an inspector would typically go into the pressure vessel in order to review its condition with the naked eye.
Most likely, the inspector will have to stand on scaffolding to complete the inspection, since the pressure vessel will be too tall for all of it to be accessible to their eye simply by standing on the floor of the vessel.
This means that inspectors face at least two hazards during their work: the need to enter a confined space, and the need to stand on scaffolding.
But an indoor drone made for inspections like the Elios 2 can replace the need for the inspector to physically enter the vessel for the purpose of visual inspections, thereby eliminating these hazards to the inspector.
It is important to note that not all drones can completely take the place of an inspector.
While some drones can provide support during indoor inspections, most drones on the market are not made for flying in confined spaces, and don’t have the unique cage design, collision tolerance, stabilization, bright lighting, and other features required to eliminate the need for an inspector to enter a confined space altogether.
It is also worth noting that using a drone for a visual inspection in a confined space only eliminates the hazard for the inspector. Those maintenance workers who will be called in to address any defects in the asset found during the inspection will still need to be exposed to the hazards listed above, since they’ll still need to enter the asset to perform their maintenance work.
EXAMPLES OF DRONES ELIMINATING HAZARDS IN INDOOR INSPECTIONS
Here are some examples of ways that the Elios 2 has eliminated hazards for inspectors conducting indoor inspection missions.
1. Scrubber inspection—Oil & Gas
The TVA (Tennessee Valley Authority) used the Elios 2 to improve safety by eliminating the need for inspectors to enter a gas scrubber and stand on scaffolding erected 55 meters (80 feet) in the air at the Cumberland Fossil Plant.
Watch the video below or read the case study to learn more.
2. Chimney Inspection—Power Generation
DTEK, the largest private investor in the energy sector in Ukraine, used the Elios 2 for a chimney inspection at one of its power plants, eliminating the need for inspection personnel to climb 180 meters (590 feet) up the chimney.
Watch the video below or read the case study to learn more.
3. FCC Unit Inspection—Oil & Gas
Tüpraş, Turkey’s largest industrial enterprise and the 7th biggest refining company in Europe, used the Elios 2 to inspect an FCC unit, eliminating the need for inspectors to enter confined spaces in the riser and cyclones by rope access.