Safety professionals know that managing heat stress is critical for ensuring both worker safety and worker comfort.
I have helped companies and their employees deal with heat exposure in different industries. One of my biggest challenges, however, was tackling heat hazards in open pit mines. The reason for that is simple: the physical environment in an open pit is itself a major contributing factor to heat stress.
How the Open Pit Climate Affects Heat Risks
An open pit mine is basically a hole in the ground – sometimes, a very big and very deep one. The air may circulate well at the surface level, but the air circulation is very much reduced by the time you reach the pit floor. There's no real chance of a cooling breeze.
Then there's the color. An open pit coal mine, for example, is full of black and dark brown surfaces. Those dark surfaces are great at absorbing heat, retaining heat, and reflect heat around.
in Fitting the Task to the Human, Kroemer and Grandjean list the following as the "climate" in the work environment:
- Air temperature
- Temperature of surrounding surfaces (and equipment)
- Air humidity
- Air movement
- Air quality
- Sunlight
- Weather
The climate of an open pit can result in ambient temperatures that make even light physical work far more difficult. This raises the risk for heat-related illnesses and requires heat mitigation and cooling strategies, along with work/rest cycles, close monitoring of workers, and adequate hydration.
To illustrate this, consider a typical office worker who typically performs light work in a climate-controlled environment. Their risk of suffering a heat-related illness is very low.
Now, let's take the same worker and move them to a mining pit. Have them do the same light work they would normally do at their desk. Only now, they're doing it outside, on a cloudless and sunny day at 90ºF and 40% humidity.
That sounds bad enough, but there's more.
DHHS (NIOSH) Publication No. 2017-127 provides a great basis for calculating the real temperature. In short, we need to add 13 degrees for full sun and 3 degrees for 40% humidity. That puts the ambient temperature up to 106ºF.
Based on these numbers, NIOSH recommends putting a worker with light work duties on a 45/15 Work/Rest cycle. But that is based on a few assumptions: that the worker is well-rested, fully hydrated, and under 40.
On top of that, we have to factor in the heat coming from the machinery and equipment used in the mining process. The protective clothing and PPE worn by the worker can also amplify the risk. Coveralls, hardhats, eye protection, safety footwear, and everything else a worker wears to stay protected add to their cumulative heat load.
(Learn more in A Sweaty Situation: PPE, Hydration, and How to Manage Both)
Acclimatization is yet another factor that needs to be considered. An old quarry supervisor of mine used to tell new workers that they would toughen up and get used to the heat. There's some truth to that – it can take at least six or seven days before getting accustomed to the open pit climate. But telling workers to toughen up isn't going to cut it – workers can succumb to a heat-related illness in a matter of minutes, no matter how "tough" they are.
Keeping Workers Safe from the Heat
Given how hot open pit mines can get, how can safety professionals keep workers safe?
Jurisdictions generally use the TLVs in the ACGIH's Heat Stress and Strain document. This publication also provides a screening tool for exposure limits for work done in hot environments. These should give you general guidance for managing heat stress.
Your approach to heat stress management should have a few different facets, including:
- Engineering controls
- Administrative controls
- PPE
- Training and education
(Learn more in A Primer on Engineering Controls)
Worker Monitoring
Education and training will give you the biggest bang for your buck. Ensuring that your workers know how to look out for each other and spot the signs and symptoms of heat stress before they become too severe is one of the best ways to prevent serious cases of heat-related illness.
Experienced workers can often judge their heat exposure far more accurately than those who are newer to working outdoors. Making sure new workers are paired up with experienced employees will ensure that there's always someone around who can spot the early warning signs.
(Learn about the 6 Key Signs of Dehydration Workers Should Know)
Administrative Solutions
For administrative controls, consider starting work early and shutting down operations during peak daily temperatures (around 1:00 to 3:00 PM). Planning the work for evening or night shifts is another effective strategy.
You will need a means of monitoring and communicating environmental conditions. The temperature at 7:00 AM can be vastly different than the temperature at 1:00 PM, but it's not always easy for someone working outside in the heat to notice that gradual change. When I worked in open mining operations, we had a big thermometer on the wall of the lunch shack. Now, all you need is a reliable app.
Be sure to have an internal reporting system in place for anyone who shows signs or symptoms of heat stress. Document and review the information acquired through this system daily.
You'll also need an emergency response plan to ensure that overheated workers can be cooled down and given first aid or other medical attention as if required.
Hydration
The human body cools itself by sweating. All that additional fluid leaving the body needs to be replaced. Good old-fashioned water is your friend here, but you can also supplement by drinking electrolyte beverages.
(Learn more about Electrolytes: What They Are and Why They Matter for On-the-Job Hydration)
Fluid intake should be equal to the amount of fluid lost. Drinking a cup of water every hour is a good place to start, even for workers who don't feel thirsty (dehydration often starts to set in before thirst does).
The best way to ensure that workers drink enough during a shift is to make sure there is a good supply of potable water on hand. Frequent reminders to hydrate are also helpful.
Cooling PPE
Cooling PPE is another great way to regulate body temperature on the job.
These come in various forms. There are cooling pads and warps that can be inserted into a hardhat to beat the heat. Cooling towels can also provide relief. Vests that are equipped with cooling packs are yet another way to keep the body cool.
Other types of cooling PPE use evaporative technology to lower the temperature. As the water in the garment evaporates, it creates a cooling sensation that helps prevent heat stress.
Design the Jobsite with Heat in Mind
Any shade you can provide will help reduce the risk of heat stress in the pit. Even standing under a parasol can make you feel 10 – 15 degrees cooler. While it doesn't protect against the warm air, the shade blocks exposure to solar radiation, which can make a significant difference.
Where possible, mechanical heat shields should be installed on any equipment that runs hot. This will minimize the impact of the heat generated by the machines on the workers who operate them.
Set up cooling stations so workers can get a break from the heat during their rest cycles. It should provide ample shade, places to sit comfortably, and a good supply of drinking water. NIOSH recommends that workers should be allowed to remove PPE while resting, including coveralls and other additional layers of protective clothing. With that in mind, it's a good idea to make sure your cooling station is located away from hazards that would make that PPE relevant.
Keeping Workers Safe from the Heat
Mining pits might be out in the open, but that doesn't mean they have the same heat risks as the surrounding outdoor areas. The atmospheric conditions in the pit, the presence of heavy machinery, and the absence of a breeze all work together to create a surprisingly hot work environment.
As a safety professional, this needs to be approached seriously. That means, in part, acquiring a working knowledge of all the relevant subject matter. HIt the books, including the National Safety Council text, the Fundamentals of Industrial Hygiene, and the ACGIH's text on TLVs and BEIs.
Those will give you the knowledge you need to confirm that your control methods are adequate. Because supplying shade and drinking water is essential, but it's not always enough.