Heat Related Illness


A 33 year old male employee is working on general housekeeping on the back side of number 2 paper machine for dust control.  He is 5’9” and 190lbs, the work environment is 85F with 86% humidity. After working for 30 minutes without having anything to drink, he is covered in sweat and feels a headache coming on and is becoming dizzy.

Which of the following options should he take?

  • Leave the work area and go rest
  • Go drink water slowly
  • Make an incident report to his supervisor or the safety manager.

The answer, as you will see from this training, is yes to all of his options.

This month’s training topic covers the dangers of work in heated and humid environments. Just ahead of our annual outage and the summer weather that follows, we are going to cover the signs, symptoms and examples of heat related illness.

Thermo-regulation: The human body is always trying to keep itself at its ideal temperature of 98.6F. Heat related illness happens when our bodies fail at keeping this internal temperature from rising.

Minor Heat Disorders: These disorders include heat rash, dehydration, and mineral loss.

Major Heat Related Illnesses:  These illnesses include heat cramps, heat exhaustion, and heat stroke. These illnesses are all directly related to the air temperature and relative humidity that a person is exposed to while working.  (See Figure 1) These illnesses can all be severe or even fatal in the case of heat stroke. It is very important to understand that heat stroke can occur suddenly and without any symptoms of heat exhaustion.

Figure 1

heat illness

Applying Critical Error Reduction Techniques  

Avoiding any heat related illness requires us to closely follow the Critical Error Reduction Techniques (CERT) principles. Rushing is the most apparent of the states to avoid. It will only produce more heat in the body and increase the risk of a serious heat related disorder.

Fatigue and heat go hand in hand, so when our bodies are already hot, fatigue can happen much sooner. It is important to understand that the rest times, which are different from employee breaks, are a proactive tool to help prevent illness, and along with fluid intake, must not be ignored.  Rest time can include light work away from the work area with the higher level of heat stress. The object is to let a person’s body cool down some and recover from the heat stress of work.

We all know it can be much easier to get frustrated when we are uncomfortable and heat and humidity top the charts. Because the heat and humidity can make us prone to frustration, we often push ourselves harder to get the job done faster. However, this only leads to additional stress and sets you up for a heat related illness, so we always need to do a mood check when working at high heat levels.

Complacency does not just mean we all have our heads down and just plow through our workday. It can mean assuming that each task we have done in a hot environment in the past will go the same way this time or the next. It can prevent us from seeing that we have changed individually. Our age, medications if any, weight, or a specific medical condition can give us new challenges.

Note: Medications can change how a person reacts to heat stress. It is always a good idea to ask your pharmacist or doctor about heat-related side effects, especially when originally prescribed when heat was not a factor, like during the winter.

CERT Principles help to show us that dealing with heat related illness is mostly about work behaviors. The planning of a job, its completion, and follow up all depend on focusing on the details of exposure to our hot environment. Leaving chance in the mix will only lead us to take unnecessary risks and potential illness.


Combating heat related illness is done by addressing personal and company behaviors.  Looking at individual health, addressing the work environment, and personal protective equipment will help everyone avoid serious heat related illness.

Fluid replacement is the MOST import way to protect your body and to protect your body’s temperature regulatory system and to prevent a heat stress disorder (see figure 3). You must take in as much fluid as you lose during work and replace the mineral salts your body uses up during sweating. Ideally, you should drink five to seven ounces of cool water every 15 minutes, even when you are not thirsty.

A reliable way to know if you are drinking enough is to look at the color of the urine being produced (see figure 2). The darker the color the more urgent is the need to drink more fluids. Being thirsty is a lagging sign of the need to drink. By the time, you are thirsty under heat stressed conditions you are already dehydrated.

Figure 2

urine color chart

Avoid hot meals as they add to your body’s heat load. Also heavy meals keep your blood in your core and away from the cooling effects of your arms and legs. Eat light meals, plan on cool foods with just a touch extra salt, unless you have been put on a low sodium diet.

Developing tolerance to the heat and humidity can prevent heat stress illnesses. The body develops a resistance to the effects of heat stress gradually over time while working in a hot environment. This gradual adjustment takes from five to seven days and is necessary for the body to become used to the physical work in a hotter environment. Unfortunately, the body has to go through the same cycle after any vacation time or medical leave.

If a person has had heat exhaustion or heat stroke, the body is now at greater risk for heat related illnesses.  Letting your current supervisor know of previous instances of heat-related illness can help them with planning and monitoring your work day.

Work-to-rest cycles are the set of behaviors that depends both on the employee and the supervisor who planned the day’s work. The warmer the heat index, or apparent temperature, the longer the rest periods become in order to combat the level of stress the body experiences (see Figure 3).

Personal Protective Equipment

Personal protective equipment is our last line of defense from various work place hazards. However, all PPE comes at a price, comfort and capacity. PPE can put addition stress on the body by making it more work to breath, in the case of a dust mask, or specifically to this topic make the body hotter.  There are specialty items that will help with heat stress. Things like hard hat coolers, bandana’s that cool you by evaporation of water, or special vests that have a fluid in them that can be frozen before the start of hot work or ones that have pouches to place ice in. The draw back with all of these types of PPE is that they are not close to being 100% effective, don’t last long and can be a pain to have to deal with.

Figure 3


Figure 4



Break into groups of 3-5 people, read the scenario, then use figure one to determine which illness is present,  then what response should be.

Recognizing the Symptoms

You are working as a Mill intern for the summer. It is very hot today as most every day in Mil. You drink plenty of water throughout the day, but you’re still thirsty and sweating a lot, although your skin feels cool.  You after your fifth trip to get samples from the wet end of #1 PM you feel weak, so you go rest for a few minutes in an air conditioned place and get a salty snack. However it’s time for you to go get another sample. As start to walk through the dryer section you feel yourself stop sweating and your face becomes flushed and hot. You have a rapid, weak pulse.

  • What are the symptoms?
  • What is the illness?
  •  What treatment or response is needed?

You have been driving a lift truck for 8 hours. You have been backing in and out of trailers for almost all that time at with a Heat index of 103F (see figure 4). When you finally get down to take a scheduled break you notice just how sweaty you are and then you say a few choice words because your left leg has suddenly cramped up into a solid mass of pain.

  • What are the symptoms?
  • What is the illness?
  •  What could you have done to prevent this from happening to you?

You are working at the dry end with the Back Tender. It’s a hot day with a heat index of 117F (see Figure 4) and you have both been sweating a lot during your shift. You notice that they are looking pale and uncomfortable.  You notice that they have not been drinking that much and when they stand up to make a machine adjustment that they are a bit unsteady.

  • What are the symptoms?
  • What is the illness?
  • What could you have done to them prevent this?

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