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Conducting work in hot environments is a serious business. Without correct workplace procedures and risk assessments in place workers can develop heat illnesses, the most severe consequences of which being death.
Mr Mtimkulu attended his pre-employment medical during the late weeks of Spring, having applied for the position of furnace attendant at an aluminium foundry in Limpopo, South Africa. The 46-year-old African Male, who grew up in the Western Cape, was not used to the hot environment of Limpopo province. During his medical examination, it was established that his height was 1.71m and he weighed 88kg. He was on treatment for high blood pressure; he could not remember the name of the tablets but promised to bring them to the clinic as soon as he had a chance. The medical staff was not too concerned, as his blood pressure was 120/80 and all other examinations were also within the normal range. While taking his medical history he stated that except for his blood pressure medication he still needed to complete a course of antibiotics, as he fell from his bicycle the previous day. The treating general practitioner issued him with the antibiotics and administered a tetanus injection on the day of the visit. He admitted to smoking about 40 cigarettes per day.
Mister Mtimkulu then attended the general induction training followed by the plant specific induction the next day. At the plant, he was responsible for turning on and attending to one of the furnaces where the aluminium gets melted.
Nearing the end of his first week at work an aluminium spillage occurred, of which the incident is still under investigation. On the day of the incident the outdoor dry bulb temperature was 28.3°C, the environmental workplace temperature was 29.4°C and the temperature of the molten aluminium inside the furnace was an estimated 982°C.
For reasons still not known as the case is still under investigation, Mister Mtimkulu decided to clear up the spillage himself. He was wearing a silver reflective suit to protect him against the radiant heat emanating from the hot metal. He then reported the spillage to his supervisor and asked permission to go to the rest room to drink some water. A co-worker discovered him on the floor of the rest room having seizures. The emergency team of the foundry transported him to the nearest hospital, where on arrival his body temperature was 42.1°C. He was admitted to the intensive care unit, but passed away the following day.
The autopsy report was requested by the Occupational Medical Practitioner employed by the furnace company. The autopsy revealed that the cause of death was hyperthermia, consumptive coagulopathy and coronary arteriosclerosis.
Taking the above case study into consideration, one needs to distinguish between a condition that threatens the health and safety of a worker, and just a feeling of discomfort when working in a hot environment.
Assessing the risk
Risk factors that need to be accessed during the risk assessment include:
- Air temperature, air movement and humidity
- Level of work activity, i.e. light manual labour versus hard physical labour
- The type of clothing and footwear
- Levels of fluid loss and replacement
- Source of radiating heat
- Work-rest cycle times
Risk factors can be divided into personal and environmental risk factors.
Personal risk factors include:
- The level of the physical activity
- The exposure time of the physical activity
- How many and what type of protective clothing is worn
- Type of clothing and footwear
Environmental risk factors include:
- Air temperature
- The level of humidity
- The level of air movement
- Radiant heat
The body’s cooling process
The major organs in the torso and muscle groups are responsible for producing about 90% of the body’s heat. If the body works harder, the heat generated by the body will increase. In humans, the average core body temperature is 37°C. For the human body to maintain a constant core temperature, the body will give up or retain heat as necessary. There are two methods in which this goal is reached: convective and evaporative body cooling.
In convective cooling the heat is removed from the body by the movement of air. The core heat is carried by the circulatory system (the system that circulates blood and lymph through the body) to the skin. Heat will always travel from hot to cold and therefore the body heat is carried to the cooler areas of the skin to assist the body in cooling down. The more blood that is pumped to the skin, the less blood is pumped to the brain. Movement like standing up or squatting can then cause dizziness, resulting in injury.
Evaporative body cooling takes place when the outside temperature rises and the difference between the normal skin temperature and the ambient temperature narrows. This difference is called Delta T. When the outside temperature rises the Delta T difference is not big enough to allow for the internal body temperature to flow away from the body by means of the convection process. Sweating follows, assisting the body in adjusting to the heat environment.
For the body to sweat the environment must be dry and warm to enable the process of evaporation. Sweating therefore speeds up the process of heat leaving the body. Should the humidity rise, perspiration can no longer evaporate to water and the cooling down process of the body will be affected negatively. This type of environment can be life threatening as the body has no other means of giving up heat generated.
Types of heat induced illnesses
The following are types of heat induced illnesses, their symptoms and initial treatment.
Heat rash
The skin will present with red papules and will usually appear in areas where clothing is restrictive. As sweating increases, a prickly / itching sensation may develop where the rash appears. If untreated, the area may become infected. The rash will mostly disappear as soon as the person is removed from the hot environment. To prevent heat rash bathe daily and keep the skin clean and dry.
Heat cramps
Heat cramps result from the loss of a large amount of salt, electrolytes and water and are associated with cramping in the abdomen, arms and claves. When a person experiences heat cramps, the following steps can be taken:
- Rest in a cool, well ventilated area or move into the shade
- Loosen all tight clothing
- Drink at least 600 ml of water every hour when working in a hot environment
- If the symptoms do not go away, seek medical assistance
Heat fatigue
Lack of acclimatisation is one of the most common causes of heat fatigue. It is therefore imperative that employees undergo a process of acclimatisation before being exposed to a hot working environment. Impaired working performance, loss of mental alertness, and loss of skilled sensorimotor functions (receiving the sensory message through vision, hearing, smell, taste, touch, sense of balance and proprioception – the sense of the relative position of the neighbouring parts of the body and strength of effort being employed in movement) can all be risk factors to consider when a person complains of being fatigued because of being in a hot environment.
Heat exhaustion
Heat exhaustion is most likely to occur when the body temperature of a person rises above 37°C but stays below 40°C. The signs and symptoms are:
- Heavy sweating
- Dilated pupils
- Intense thirst from dehydration
- Fatigue
- Skin clammy and pale
- Dizziness
- Headache
- Nausea and/or vomiting
- Weak rapid pulse >120 – 200 beats per minute
- Blood pressure low to normal
- Impaired judgement
- Hyperventilation
- Fainting
Victims of heat exhaustion must be examined by a qualified medical practitioner and should be kept on bed rest for the remainder of the day. Restoration of body fluids, salts and electrolytes will be taken care of by the medical practitioner. Until such medical assistance is available, the following should be done:
- Call for help and get someone to call an ambulance
- Move the victim to a cool, well ventilated or shaded area
- Loosen or remove clothing and boots
- Cool the victim down with cold wet water if available, as it dissipates heat 20 – 30 times faster than cool air
- If available direct a fan at the victim
- Lift the victim’s legs and massage the limbs
- If available and the victim is still conscious, have them drink water with a flat teaspoon of salt added to the water.
- Stay with the victim until medical help arrives
Heat stroke
If not treated quickly and effectively, heat stroke becomes a serious heat related condition. The body temperature will rise above 40°C. This is a medical emergency and anyone with heat stroke should be admitted to a hospital immediately. It may initially look like heat cramps or even heat exhaustion, but the rapid deterioration of the victim will clarify the matter as a heat stroke. The signs and symptoms of heat stroke are often masked. For example, a cool skin can mask a high core body temperature and on the job collapse can be mistaken for a heart attack. This is especially the case if the heat stroke is caused by exertion as the victim may still be sweating.
Early symptoms:
- Body temperature above 40°C
- Absence of sweating in most cases
- Skin dry, hot and appears flushed
- Rapid pulse
- Difficulty breathing
- Constricted pupils
- High blood pressure
- Headache
- Dizziness
- Confusion or delirium
- Weakness
- Nausea or vomiting
Advance symptoms:
- Seizure or convulsions
- Collapse with loss of consciousness
- Deep coma
- No detectable pulse
- Body temperature of > 42.2°C
Follow the steps in treating the heat exhaustion victim, ensuring that you lower the body temperature as fast as possible. It is imperative that you do not give the victim anything to drink if unconscious. If the means is available, immerse the victim into cold water and massage the body with ice.
Hazards of hot environments
Direct causes of accidents include, but are not limited to:
- Fogged glasses
- Sweat dripping into the eyes
- Sweaty palms
- Dizzy spells
- Fainting
Indirect causes of accidents may include, but are not limited to:
- Irritability and anger
- Poor judgement
- Loss of concentration
- Physical discomfort
- Slowed response time due to mental and physical fatigue
Managing the risk
The risk of heat stress in the workplace is very real and can be life threatening, but can be managed through acclimatisation and appropriate workplace procedures.
Acclimatisation
Acclimatisation is the ability of the body to perform a maximum amount of strenuous work in a hot environment by gradually exposing the employee to such an environment, increasing the exposure time over a period of at least a week. During this week, hard physical labour time should be alternated with lighter work and longer resting periods. Some workers may need a longer period to acclimatise. Most workers will be fully acclimatised after a month of work in a hot environment.
Workplace procedures
A procedure should be in place providing the steps to follow to ensure that a worker is safe when working in a hot environment. The procedure must at least address the following:
- Work-rest cycles.
- Altering of light and heavy work when reasonably practicable.
- Training in heat hazards and the prevention thereof.
- Scheduling of employees for medical examinations.
- The need for getting an approved inspection authority (AIA) to measure the wet bulb globe temperature (WBGT) and the intervals of these measurements. The WBGT index is calculated using a formula that considers air temperature, speed of air movement, radiant heat from hot objects, sunshine and body cooling due to sweat evaporation.
- Fluid intake, i.e. if the WBGT index is greater than 30 and manual labour needs to be performed, the worker must be provided with cool drinking water and must drink at least 600ml of water every hour.
- The outcomes of occupational hygiene surveys indicating the WBGT indexes and what areas in the workplace should be regarded as a hot working environment.
- Personal protective equipment required to wear before entering a hot working environment.
- Alcohol consumption dehydrates the body and employees should be discouraged from using alcohol as it can exacerbate heat stress effects.
- Eating habits of the heat environment worker. Hot foods add to body heat as it redirects blood flow to the digestive tract instead of the skin. The meal that is taken during the workplace lunchbreak must be a light and cool meal and the worker should rest after the meal.
- Normal salt intake for an acclimatised worker will be sufficient when working in hot environments.
- The emergency action plan must be known by every employee.
- The weight of a self-contained breathing apparatus (SCBA) will increase the overall heat stress of a worker.
Hot work considerations
The following are factors that need to be considered before allowing a person to work in a hot environment:
- Prevention of dehydration –ensure that drinking water is readily available and that employees indeed drink 600ml of water per hour
- Improper work procedures and the prevention thereof
- Lack of sleep
- Not fully acclimatised
- Restrictive clothing
- Recent use of alcohol < 24 hours prior to shift
- Special care needs to be taken during the medical examination if the heat worker employee is using anyof the following medication:
- Using any abusive drugs
- Anaesthetic agents
- Anticholinergics
- Antihistamines
- Sympatholytic / anti-hypertensives
- B-blockers
- Diuretics
- Lithium
- Monoamine-oxidase inhibitors
- Phenothiazine
- Salicylates
- Stimulants
- Using tablets for thyroid hormone
- Sympathomimetic
- The medical practitioner doing the assessment of Fit to Work also need to take the following into consideration:
- A person between the age of 50 – 65 is more susceptible to heat stroke
- Body-mass index (BMI)
- A BMI of > than 30
- A BMI of < 16
- History of heat disorders should be re-considered to be declared Fit to Work in a hot environment
- Document the JACCOL (Jaundice, Anemia, Clubbing, Cyanosis, Oedema and Lymphadenopathy) in full on the medical file of the heat worker by specifying any findings.
- Contra-indications to declare a person Fit to Work in a hot environment will therefore be:
- The BMI index above or below minimum medical standard for fitness
- Medical contra indications, i.e. a medical condition under treatment that may increase the risk of heat exposure related disease, medical history that can lead to a critical work-place reduction in heat tolerance
- Any heart disorders or history of a heart disorder
- Insulin dependent diabetic
- Persons above 50 years of age
- Since a person with diarrhoea and/or vomiting will not necessarily report to the medical station, workers need to be trained to report this conditions to the supervisor who must then first send them for Fitness Assessment by a medical practitioner before allowing them to work in a hot environment
Workloads defined
- Rest – environment where the person sits while performing work with moderate arm movement
- Light work – the person may be sitting or standing; performing light hand or arm work with occasional walking and even driving
- Moderate work – the person does moderate lifting / pushing / pulling; walking at a moderate pace
- Heavy work – shovel work, digging, lifting / pushing / pulling heavy objects; walking at a fast pace
- Very heavy work – very intense activity at a maximum pace
Control measures
Engineering controls:
- Reduce metabolic heat production by automation and mechanisation
- Reducing radiant heat emission
- Reduce the humidity
- Insulation of hot surfaces
- Shielding
- Ventilation and air-conditioning
Administrative controls:
- Sufficient acclimatisation periods
- Work/rest cycles
- Provide cool rest areas
- Allow workers to set their own pace is reasonably practicable
- Provide cool drinking water with easy access
- Establishment of emergency procedures and provide trained first aiders
PPE:
- Eye protection for radiant heat
- Reflective clothing
- Auxiliary body clothing
