Health & Safety Planning Under OSHA's Heat Illness Regulations 2024

With the arrival of the summer months, temperatures rise, an increased amount of activity and maintenance takes place outdoors, and heat and humidity creep into indoor working areas. For businesses based in warmer and temperate regions, this transition to hotter weather can entail the risk of heat illnesses and the need for an additional set of precautions and measures to avoid them.

In fact, heat is the deadliest of all hazardous weather conditions in the United States, and the existence of related adverse health effects has led OSHA to propose rulemaking to address them. Titled "Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings" and published in the Federal Register on August 30th, 2024, the proposed rule seeks to set the first nationwide standard of its kind and would apply to "all employers conducting outdoor and indoor work in all general industry, construction, maritime, and agriculture sectors where OSHA has jurisdiction".

This article presents an overview of heat illnesses to which employees may be exposed on any given summer workday, the response measures that should be taken immediately after noticing any symptoms of these illnesses, the responsibilities for employers under OSHA's new rule, and a few governmental guidelines for Canadian counterparts.

Please use the table of contents below to navigate to the section most relevant to you.

Table of Contents

What are the 6 Main Types of Heat Illness?
Response Measures: Reducing Internal Body Heat Immediately
What is OSHA'S New Heat Illness Regulation?
Employer Responsibilities Under OSHA's Heat Regulations 2024
-How to Recognize Heat Hazards and Heat Stress Situations
-Heat Illness and Injury Prevention: Work Practices
-Heat Illness and Injury Prevention: Engineering Controls
-How to Protect Employees Under OSHA's New Heat Regulations
Heat Illness Guidelines for Canadian Employers Under OH&S Standards: Ontario
-Time-Weighted WBGT Values and ACGIH Heat Stress Screening Criteria

What are the 6 Main Types of Heat Illness?

There are a variety of heat-related illnesses (also known as hyperthermia) that could affect an employee working in hot weather conditions. They all generally stem from exposure to a combination of environmental heat (produced by the surroundings) and metabolic heat (produced by exertion) that overpowers the human body's ability to cool itself down.

The list below presents the main heat injuries and illnesses, along with some of their symptoms, sorted in increasing order of severity.

• Heat rash: red, itchy bumps on the skin
• Heat edema: swelling, especially around the ankles
• Heat cramps: muscle pain in overworked areas, such as arms, legs or stomach (caused by salt imbalance from heavy sweating)
• Fainting (caused by fluid loss and lack of water)
• Heat exhaustion: elevated body temperature due to the body's inability to cool itself, leading to nausea, dizziness, muscle cramps, headaches, and heavy sweating
• Heat stroke: a complete breakdown in the body's inability to dissipate heat, leading to internal temperatures of 105.8 °F (41 °C) or more; symptoms include a rapid heart rate, confusion, slurred speech, seizures, and unconsciousness
  • Classic heat stroke: occurs when people lose the ability to sweat and are not very physically active when ill, primarily as a result of passive exposure to extreme heat
  • Exertional heat stroke: occurs as a result of strenuous physical exercise during which people are still active and sweating

Employers and employees should be on the lookout for these symptoms in any situation during which they feel they are working under conditions of heat stress (more on recognizing these conditions in the sections below). They are also required to keep up-to-date records of the occurrence of these illnesses, i.e. an audit trail, through the use of a reliable incident management system.

Response Measures: Reducing Internal Body Heat Immediately

Whatever the rules for monitoring and prevention may be, there is really only one thing to do when someone exhibits the symptoms of one of the heat illnesses above: cool that person down.

OSHA recommends taking them to a shaded or air-conditioned (or otherwise cooler) area, using fans to circulate the air around them, removing any outer layers of clothing, and placing ice packs or cold wet towels on their head, neck, armpits, trunk, and/or groin.

If the symptoms are more severe (for example, heat exhaustion) and you find yourself in an emergency, you should immerse the affected worker in cold water or an ice bath to quickly lower their body temperature.

In cases of heat stroke, as evidenced by seizures, slurred speech, or unconsciousness, follow the recommendations above and call 911 immediately. Without immediate first aid, heat stroke can result in permanent brain damage and even death.

Also remember to never leave the affected person alone! Heat illnesses can worsen rapidly and require further intervention from the supporting workers.

Lastly, you should consider logging the incident into a centralized management system that analyses its root causes, eliminates time delays in mobilizing a response team, and helps prevent future occurrences with CAPA management and comprehensive reporting.

What is OSHA's New Heat Illness Regulation?

Recognizing the effects of climate change on temperature across the USA, the prevalence of heat injuries and illnesses (~3,400 each year), and the fact that any statistics for these phenomena are likely vast underestimates, OSHA has proposed the "Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings" rule.

Under the new rule, employers in the four targeted sectors (general industry, construction, maritime, and agriculture) will be responsible for protecting workers whenever work activities are performed at or above the initial heat trigger of 80 °F (26.66 °C), or whenever there is reasonable expectation of exposure at or above that heat trigger. They would also be legally required to "evaluate and control heat hazards in the workplace" and set forth measures to protect them from excessive heat.

Before we dive into the multitude of requirements proposed by the rule, it is worth addressing a thought that might have crossed your mind by now: "will this actually become law?".

At the time of writing, the rule has made it through the comment period and is waiting for its informal public hearing on June 16th, 2025. How much of the proposed rule will become legal requirement is anyone's guess at this stage, but whether it is widely accepted as a necessity or shot down as red tape, employers will likely have to implement its recommendations to some degree.

This is because employers are still subject to OSHA's General Duty Clause, which obligates them to take every reasonable precaution for the protection of a worker, including protection from hazardous thermal conditions. OSHA is already conducting heat-hazard inspections, and failure to abide by this general duty can result in a citation.

Employer Responsibilities Under OSHA's Heat Regulations 2024

It stands to reason that, if the goal of the proposed rule is to avoid heat-related illnesses and injuries, employers will have to do their part in ensuring employees do not "overheat" and that, if they do, there is a procedure in place to cool them down.

In short, employers have to develop a heat illness prevention plan. The plan must answer a wide range of questions, but it boils down to three essential components: recognizing a heat hazard, preventing harmful exposure to heat via mindful work practices, and instituting engineering controls that minimize the risk of a heat illness.

Let's go through each part in detail.

How to Recognize Heat Hazards and Heat Stress Situations

The first step in preventing and addressing heat illnesses and injuries is being able to determine whether a heat hazard is indeed present in the workplace. To do so, employers must evaluate the total heat stress—environmental heat plus metabolic heat—that an employee may be exposed to at any given time.

If this sounds complicated to you, it's because it is. Fortunately, OSHA has outlined a multi-step process to accurately assess heat stress.

Step 1: Using the Wet Bulb Globe Temperature (WBGT) Index

To measure environmental heat, you must quantify four factors: air temperature, relative humidity, radiant heat (from sunlight or artificial heat sources, such as furnaces), and wind movement (given that a lack of wind equates to less cooling off).

Rather than recommending that you try to measure each factor independently, or that you rely on your city's heat index value (which only accounts for the first two factors), OSHA suggests you purchase a wet bulb globe temperature (WBGT) monitor. The monitor measures ambient air temperature, the potential for evaporative cooling, and radiant heat by utilizing a dry bulb thermometer, a natural wet bulb thermometer, and a black globe thermometer (respectively).

A picture of a WBGT device, with emphasis on its three thermometers (taken from the OSHA website)

You simply place the WBGT device on site where the workers are (ex: outside and under the sun) and let it sit for 20-30 minutes to allow the thermometers to stabilize, then read the value on the screen.

If you are unable to obtain a WBGT device, you might get away with purchasing the three thermometers separately and combining the readings using one of the two formulas below.

For conditions in direct sunlight: (0.7 x Wet bulb temperature) + (0.2 x Black globe temperature) + (0.1 x dry bulb temperature)

For indoor or shaded conditions = (0.7 x Wet bulb temperature) + (0.3 x Black globe temperature)

Keep in mind that these formulas are only recommendations from the Canadian Center for Occupational Health and Safety (CCOHS) and that the results of these calculations may differ from the value derived from a WBGT device.

You might also want to consider putting in place some form of data collection and analysis system that keeps track of these values and helps you fill out heat illness incident reports.

Step 2: Understanding the Clothing Adjustment Factor (CAF)

As you are probably aware, clothing serves to either retain or dissipate heat. In the winter, we wear the kind that retains it (ex: winter jackets made of down or wool), whereas much lighter clothes are essential to cool off in the summer. However, certain kinds of jobs require certain attires (coveralls, protective gear, etc.) which, in some cases, can prevent the wearer from cooling off as they should in elevated temperatures. 

In these cases, the wearer is said to experience an "effective WBGT" that feels warmer than the ambient WBGT captured by the device. The WBGT measurement must as such be adjusted by a factor, depending on the worker's clothes, to account for this difference.

Below is a short list of the adjustment factors for the different types of clothing often used in industrial workplaces:

• Cloth coveralls: 0 (i.e. no addition to the measured WBGT value)
• Spunbound melt-blown synthetic (SMS) coveralls: 0.9 °F
• Polyolefin coveralls: 1.8 °F
• Double-layer cloth clothing: 5.4 °F
• Limited-use vapor-barrier coveralls: 19.8 °F

(NOTE: This list only includes the five types of clothing accounted for in the National Institute for Occupational Health and Safety (NIOSH) guidelines cited by OSHA in their Heat Hazard Recognition webpage.)

Step 3: Considering Acclimatization and Protecting New Workers

Simply put, acclimatization refers to the process by which a worker becomes accustomed to a new climate, new weather conditions, or a new environment. As far as exposure to higher temperatures goes, it entails developing a higher sweating rate, a lower body temperature, an increased flow of blood to the skin, a lower heart rate, and a significant decrease in salt loss through sweat (which prevents muscle cramps).

Acclimatization is a crucial component of the heat risk calculation because around half of all heat-related deaths occur on a worker’s first day, and over 70% during a worker’s first week!

Considering the elevated risk, employers are expected to provide new employees, those who return to work after a prolonged absence, and those who work on days when the weather is "significantly warmer than on previous days" (such as during a heat wave or when temperatures first begin to increase in the spring or early summer) a period of two weeks to acclimate. That means significantly shorter workdays with more rest periods, all the while performing tasks that are similar in intensity to the expected work.

One possible (and OSHA-recommended) arrangement is to follow the "rule of 20%".

On the first day, the worker performs intense tasks up to 20% of the normal duration, i.e. 1 hour and 36 minutes for an 8-hour workday. The rest of the time is spent resting or on work that expends minimal energy.

On the worker's second day, the time spent on intense tasks increases by 20% (to a total of 40%), and so on, with an additional 20% added on each subsequent day. By the end of the first week, the worker should be acclimated and therefore capable of working at the same intensity and for the same duration as the experienced workers.

However, the one-week timeline is only an estimate. Some workers, such as those who are not physically fit or who have any of the personal factors listed above, will require more time to adapt.

The main thing to remember is that these limits must not be exceeded. If a worker feels like he or she needs more than one or even two weeks to adjust to the hot temperatures, give him/her that time, but the opposite should not happen -- workers who express a desire to work past the 20%, 40%, 60%, or 80% limit should be prevented from doing so.

The reason for this stipulation is found in human nature. New workers often internalize external pressures to perform or fit in and, as a result, overexert themselves, either by pushing past their physical limits or ignoring heat-related symptoms. In other words, employers cannot rely on them to self-acclimate... which is why a lot of companies pair them up with existing employees in a sort of buddy system where there is always at least one person present that could perceive and act on symptoms of heat illness or injury.

Step 4: Determining Heat Stress Based on Workload

Once you have measured the environmental heat at the work area with a WBGT monitor, converted the reading into the effective WBGT value by adjusting for the employees' clothing, and determined whether any employees (and how many) are acclimated, you may proceed to check for the existence of potential heat stress.

To do so, check the effective WBGT value against the employees' workload on the table below. (If you're unsure which workload level corresponds to the activities your employees are performing, refer to the "Metabolic Heat and Workload" section of OSHA's Heat Hazard Recognition webpage.)

Table taken from OSHA's Heat Hazard Recognition webpage, itself an adaptation of NIOSH guidelines

Whenever the effective WBGT you have measured is at or above either the action limit (for unacclimated workers) or threshold limit value (for acclimated workers) at their current workload, then the heat stress at your facility is too high. Workers should either decrease their workload, take more frequent and longer (water) breaks, or stop working altogether.

How much of a reduction in work will ultimately be determined by you, the employer. When deciding which actions to take, you should operate under the principles that workers who do intense labor require more protections and that effective WBGT values significantly above the limits call for more drastic responses (such as a complete cessation of work) than smaller excesses.

Making these decisions is a lot easier when you have a wealth of data from which to draw. ERA can help you create fully customizable graphs and other KPIs to inform your decisions at a glance, or even put a system in place that tracks meteorological data at your city, inputted WBGT values, and temperature anomalies to advise you whenever a heat stress situation may exist. Speak with a dedicated Project Analyst today to know more.

Heat Illness and Injury Prevention: Work Practices

The only feeling that's better than knowing you are actively monitoring for heat stress (by following the four steps above) is knowing you have planned in advance to lessen the impact higher temperatures may have on your employees by adopting work practices that minimize their rate of metabolic heat production and their exposure to environmental heat.

The most basic recommendation to that effect is to provide plenty of shade, rest, and water. 

Workers should be under clear instructions to take mandatory breaks in a shaded and/or cooler location (such as under a tent or inside an air-conditioned vehicle) when necessary. These breaks should become more frequent and longer as heat stress rises; a good rule of thumb is to schedule mandatory hourly breaks whenever the effective WBGT exceeds the limits on the table above.

During these breaks, employees must prioritize recovering from the heat. They should not perform any other work and, instead, ensure they drink water and/or electrolyte-containing fluids (such as sports drinks) at a rate of at least one cup (or 8 ounces) every 20 minutes. Hot, sugary, and alcoholic beverages should be avoided.

For further recommendations on work and rest cycles and their optimal lengths as a function of workload and WBGT value, visit the NIOSH and ACGIH websites for heat stress.

Here are a few other work practices you can implement in your workplace to prevent overwhelming heat stress:

• Scheduling work at a cooler time of day (i.e. early morning or late afternoon)
• Minimizing manual effort and rotating job functions among workers to reduce exertion and/or heat exposure
• Rotating work activities between hotter and cooler environments
• Increasing the number of workers per shift (to cover for workers taking breaks to cool off)
• Implementing a buddy system, especially one pairing new with experienced employees
• Providing sunscreen for employees to wear and reapply regularly

Heat Illness and Injury Prevention: Engineering Controls

The other straightforward way of reducing an employee's risk of developing a heat illness or injury is to rely on technology.

Engineering controls refer to strategies that remove a hazard from the workplace or control it at the source. In the case of dealing with hotter temperatures, these controls either artificially cool down the work environment or reduce workers' workloads and, thereby, their metabolic heat production via mechanization.

Common engineering controls for combatting heat stress are:

• Air conditioning
• Air-conditioned construction equipment cabs
• Conveyors and forklifts
• The elimination of steam leaks, wet floors, and hot water baths
• Fans and misting fans
  • NOTE: Do not use fans when the air temperature is above 95 °F (35 °C), as they may recirculate hot air
• Local exhaust ventilation
• Reflective shields that redirect radiant heat
  • Stainless steel, aluminum or other bright metal surfaces that reflect heat back towards the source 
  • Water-cooled jackets made of black-surfaced aluminum, which absorb and carry away heat
• Sheets of low-emissivity material (such as aluminum) or white paint covering hot surfaces

The most common solution to the heat stress problem is air conditioning, but don't forget that any HVAC system will require some kind of refrigerant management software to guarantee compliance with EPA Section 608 of the Clean Air Act.

How to Protect Employees Under OSHA's New Heat Regulations

It is worth taking a moment to specify exactly how employers would be required to look out for their employees under OSHA's new proposed rule (as the work practices and engineering controls above are merely recommendations).

For starters, all employees would have to be trained to recognize and deal with heat-related illnesses and injuries. They have to be equipped with the knowledge to identify symptoms, apply first aid measures, follow the procedure for contacting emergency services, and determine whether a heat stress situation exists.

They should also be capable of answering the question "How do we respond when the National Weather Service issues a heat advisory or heat warning?".

Among the trained employees, there should be one working each shift whose primary function is to monitor weather conditions throughout the day and implement the heat illness prevention plan when necessary. This person can be a foreman, jobsite supervisor, safety director, or just about any other employee with the expertise and bandwidth to identify heat hazards, recognize symptoms of heat stress, and lead in first aid efforts.

Heat Illness Guidelines for Canadian Employers Under OH&S Standards: Ontario

The article so far has detailed the recommendations for heat stress prevention, monitoring, and response as outlined in OSHA's new proposed federal rule. While Canadian employers would of course not be subject to this rule, the Occupational Health and Safety (OH&S) standards for their province (to which they are subjected, unless they are federal employees) may in fact resemble them.

One such example is Ontario's "Protecting Workers from Heat Stress and Heat-Related Illnesses" guidelines, established by the province's Ministry of Labour, Immigration, Training, and Skills Development (henceforth, "the Ministry").

The Ministry is currently proposing to introduce its own heat stress regulation under the Occupational Health and Safety Act (abbreviated to "OHSA"). As with the United States' OSHA, the regulation introduces heat stress exposure limits, mandates employers to create and implement a heat stress control plan, and requires employees to be trained in symptom recognition and first aid.

As the province is more homogenous, climate-wise, than its southern neighbor, the Ministry can set more clear and universal rules for the applicability of the control plan—it would be in use from May 1st to September 30th; before and after these dates, only workplaces that can become hot with process heat, due to the presence of smelters, bakeries, furnaces, etc., would require a plan.

Employers are instructed to follow the plan on days when the humidex on site is 35 or higher, when Environment Canada reports air temperature that exceeds 30 °C and a humidex of 40, during heat waves (three days or more) at or above 32 °C, and when the Ontario Ministry of the Environment, Conservation and Parks issues a smog alert.

In these situations, employers should follow the ACGIH guidelines, which we have presented above.

Time-Weighted WBGT Values and ACGIH Heat Stress Screening Criteria

The Ontario OHSA rules, however, differ in a couple of vital respects from the US OSHA ones.

For starters, exposure limits for employees are harder to determine. Whoever is in charge of heat stress monitoring would have to calculate time-weighted average exposure values (TWA-WBGT), not just record the readings off a WBGT device. The formula is as follows:

Where:

• WBGT1, WBGT2, …, WBGTn = WBGT heat exposure values in °C for tasks 1, 2, …, n
• t1, t2, …, n = Duration of tasks 1,2, …n in minutes
• Average WBGT values are averaged over a 60-minute period for continuous exposures...
• ...and intermittent exposures or exposures at different heat levels throughout a workday are averaged over a 60 - 120 minute period, depending on the exposure duration

Similarly, the table of action limits and threshold limit values against which effective WBGT values are checked is a little more nuanced. It accounts for information on the worker's work/rest cycle and therefore allows for work during higher temperatures, provided it occupies a smaller percentage of the cycle.

Here is the ACGIH screening criteria used by the Ministry (effective WBGT values in °C):

To read this table, simply take any three of the four factors that make up the heat stress calculation (the WBGT temperature values, the employees' workload, their allocation of work in a work/rest cycle, and whether they are acclimated or not) to find the fourth.

For example, if an acclimated worker is performing moderate work as part of a work/rest cycle where 75-100% of the time is spent working, then a heat stress situation exists whenever the WBGT temperature is at or above 28 °C.

Remember, this table presents potential heat stress situations in effective WBGT values. You must incorporate the employees' clothing adjustment factor to make use of it; it can make a huge difference!

For instance, if the same worker described above wore double-layer woven clothing and therefore had an effective exposure level of 31 °C (whenever the temperature read 28 °C), that worker would only be allowed to work 0-25% of the overall workday (to avoid heat stress).

Those are the few differences we could find during our research, but they are likely a few others hidden in the official regulations.

If you're a Canadian employer, you should try to find and contact your own province's health and safety agency (for example, British Columbia's and Saskatchewan's WorkSafe programs). This is the best way of keeping abreast of changing regulations aimed at responding to a volatile climate.

And if you’re looking for a solution to help respect these new heat stress guidelines, the seasoned regulatory experts at ERA can help. Schedule a discovery call today to see how our health & safety software can handle your Incident management and prevention.