Heat Stress and Illness Prevention

What is heat stress?

Heat stress can be defined as the net heat load to which a person is exposed from the combined contributions of metabolic heat, environmental factors, and clothing worn which results in an increase in heat storage in the body. The neat heat load on the body is the total heat stress which is considered to be the sum of the heat generated in the body (metabolic heat), plus the heat gained from the environment (environmental heat), minus the heat lost from the body to the environment.

The net heat stress that a person experiences is dependent on a combination of factors such as the climatic conditions, the work environment, demands of the work and personal characteristics. A person experiences a physiological response to the heat load (external or internal), in which the body attempts to increase heat loss to the environment in order to maintain a stable body temperature.

What are the adverse effects of heat stress?

Heat stress becomes a deep concern and a critical hazard when the body becomes overwhelmed and is unable to keep up the rate of heat discharge to the environment that is required in order to maintain a stable body temperature that is vital for normal body functioning.

At some level of heat stress, a person’s compensatory mechanisms are no longer capable of maintaining body temperature at a level required for normal body functioning. As a result, the risk of heat-related illnesses, disorders, and other hazards increases. The level of heat stress at which excessive heat strain will result depends on the heat tolerance capabilities of the worker. However, even though there is a wide range of heat tolerance between workers, each worker has an upper limit for heat stress, beyond which the resulting heat strain can cause the person to become a heat casualty.

Heat illnesses that can be experienced as a result of uncontrolled heat stress include heat stroke, heat exhaustion, heat cramps, heat rash and fainting.

When do employees experience heat stress health effects?

Heat stress can be experienced at any instance and is not only restricted to the summer months and outdoor work alone. Doing strenuous work that has a high metabolic rate wearing high insulating clothing can also contribute significantly to high levels of heat stress. Similarly working in indoor environments where the ambient temperature is elevated because of the operation of heat producing equipment and systems also contribute to high heat stress levels. Furthermore, there are personal factors such as obesity, intake of caffeine and other general health characteristics that make a person more vulnerable to heat stress.

At some level of heat stress, a worker’s compensatory mechanisms are no longer capable of maintaining body temperature at a level required for normal body functions. As a result, the risk of heat-related illnesses, disorders, and other hazards increases. The level of heat stress at which excessive heat strain will result depends on the heat tolerance capabilities of the worker. However, even though there is a wide range of heat tolerance between workers, each worker has an upper limit for heat stress, beyond which the resulting heat strain can cause the worker to become a heat casualty.

How can heat stress be monitored?

Monitoring physiological response of employees is the optimal way to identify heat stress scenarios. Never ignore heat stress symptoms even if the measured environmental parameter is below the limit of the standard referenced. Proactively heat stress can be managed by monitoring the heat index of the environment in which work is being undertaken.

The heat index (HI) is a metric that combines temperature and humidity values to provide an apparent temperature. It is an approximate indication of how hot someone feels. This is a simplified evaluation method and affords good protection against adverse effects of elevated heat stress levels. For a given temperature the higher the humidity the higher the heat index. Higher humidity levels reduce the efficiency of evaporative cooling thereby reducing the rate of excess heat dissipation thereby making an individual feel warmer.

The heat index combines two measured parameters namely the atmospheric temperature and relative humidity. The two obtained values can be combined using the Chart provided below to ascertain the heat index value. The index indicates the temperature that the human body feels. When the index gives a higher temperature, the risk of sustaining heat related illnesses and other injuries increases.

What proactive actions can be taken to prevent heat illnesses?

A combination of both general and job specific controls need to be adopted to manage the risk of heat stress. Recommended actions are based on the measured heat index value. The table below provides recommended resting time and water intake for a given heat index range.

Note! 1 Glass = 250 ml. DO NOT drink more than 1.5 liters per hour (maximum water absorption rate of body)

Apart from this it is the employer’s responsibility to ensure that adequate job specific engineering and administrative controls are in place to ensure that heat stress situations are avoided. Common engineering and administrative measures are provided below.

Red Flag Measures

• When a heat index value of >56°C or higher is reached, or ambient temperature reaches 50˚C, whichever comes first, red flags are posted.
• Under the red flag condition, all non-protected work shall stop and workers shall be removed from the high heat exposure. Work can only be continued under red flag conditions for specific activities:
  1. If employees or contractor staff have a specific plan in place, including a risk assessment.
  2. Appropriate measures are approved by the Head, Health and Safety and with agreement from the PLHCP(Physician Or Other Licensed Health Care Professional).
• Approval by the Head, Health and Safety may be given for activities that cannot be interrupted such as, security cover and urgent maintenance of equipment. Approvals could also be given for areas where working conditions are more favorable, such as shaded areas and areas with wind and/or natural draft or for activities having only a light workload, but local monitoring must be undertaken.
• Special attention shall be taken to rotate workers in these conditions to allow sufficient periods of rest in a shaded or air-conditioned facility (e.g. vehicles with air conditioners) and rehydration.
• When there is a local legal requirement announced, prohibiting work between 12 noon and 3:00 p.m. (usually between 15 June to 15 September), the provisions thereof shall be implemented, regardless of what the flag color is.

What job specific engineering controls can be adopted to prevent heat stress?

A range of engineering controls can be adopted to reduce the heat index of the working environment

1. General VentilationLarge areas or entire buildings identified as high heat areas may require a permanently installed ventilation system to reduce temperature levels. In smaller areas, portable or local exhaust systems may be more effective or practical.
2. Local VentilationReduce the risk of heat illness by increasing the volume of air flow and velocity with fans and other air movers in the work area, as long as the air temperature is less than the person’s skin temperature. If the air temperature is higher than approx. 38° to 40°C, skin warming may offset any advantage gained by evaporative cooling.  Because this method does not cool the air, the increased air flow must contact the worker directly to be effective.  This control will have little, if any, positive effect on workers wearing vapor-barrier clothing.
3. Air Treatment/Air CoolingThis control measure differs from ventilation because it cools the air by removing heat, and sometimes humidity.  Air conditioning and air treatment devices may be expensive to install and operate, nonetheless, mechanical refrigeration can be effective in specific areas such as “cool rooms” used as recovery areas near hot jobs.  Portable blowers with a built-in air chiller are effective for cooling enclosures.  The main advantages of blowers are portability and minimal set-up time.
4. Radiant Heat ReductionReflective heat shields and insulation will reduce radiant heat.  With sources of radiation such as heating pipes, it is possible to use both insulation and surface modifications to achieve a substantial reduction in radiant heat.  If shields are used, it is important to minimize their inevitable undesirable influence of reducing air flow.
5. ShadeShade will reduce radiant solar heat and is a widely recognized control measure.  Shading the work area, rest areas, equipment or enclosures can significantly decrease the heat load.

What job specific administrative controls can be adopted to prevent heat stress?

Scheduling
If possible, perform potentially hot jobs when heat illness conditions are at their minimum. Allow latent heat in equipment to dissipate before work begins. When practical, schedule work for the cooler part of the day, and schedule routine maintenance and repair work in hot areas for the cooler seasons of the year.

Fluid Replacement
Place ample supplies of cooled drinking water in hygienic conditions close to the work area. Because the normal thirst mechanism does not ensure sufficient fluid intake, encourage workers to drink small amounts on a frequent basis.

Acclimatization
Most people get used to heat exposure up to a point. This is called acclimatization and it results in less cardiovascular demand for a given activity. The employee will sweat more efficiently (increasing evaporative cooling) and may lose less salt, thus will more easily maintain normal body temperature. Acclimatization decreases the risk of heat-related illnesses and associated unsafe acts. Deliberate acclimatization involves exposing employees to work in a hot environment for progressively longer periods.

For new workers who will be similarly exposed, the regime should be 20% on day one, with a 20% increase in exposure each additional day

• Prescribed periods of work and rest are based on the heat index . These prescribed levels are based on the assumption that the work is repetitive, controlled, and continuous over an eight-hour shift, and that the rest area is in an environment close to that in which the exposure occurs to avoid walking far distances to and from the work environment.
• Recovery may be required for any heat illness exposure.  Recovery is complete when the person’s physiological state has returned to its pre-exposure condition.  This means that excess stored body heat has been dissipated, lost fluid has been replaced, and electrolytes are in balance.  To permit dissipation of stored body heat, the recommended recovery area should be cool and not hot and humid.
• Appropriately, trained workers can help monitor their own heat condition.  Training should emphasize that heat illness can affect an individual’s ability to reason clearly. This may cause them to fail to recognize signs and symptoms of heat stroke.  For this reason, self-determination needs to be augmented by the heat illness program, worker-training program and check time (CT) .
• Check times are intervals at which a heat illness trained Person in Charge or observer, including a co-worker, must seek explicit confirmation from individual heat illness trained workers that each can continue work. That is, the observer determines if there are obvious symptoms of heat disorders, or if there is any sense of diminished capacity. If so, the exposure is terminated, and rest is required. Using CTs requires each worker, at regular intervals, to explicitly assess his/her physiological state and ability to continue work, rather than waiting for symptoms to appear.

Training
All employees who have the potential to be exposed to elevated levels of heat stress have to be trained periodically. It will be the Department Manager’s responsibility to ensure that appropriate training is imparted. The key topics that will have to be covered include basic understanding of the body’s physiological response to heat stress, signs and symptoms of heat stress and actions that need to be taken to avert adverse consequences of heat stress.

Other Administrative Controls
Reduce the physical demands of work such as excessive lifting or digging by using powered equipment, increase the number of workers assigned to a task, use relief workers, and limit worker occupancy in confined areas.

What specific PPE’s can be used to manage heat stress?

Personal protective equipment is not a substitute for engineering and administrative controls should not be the sole control measure to protect employees from heat stress, however sometimes PPE is required to supplement engineering controls and good work practices. Some of the PPE available include:

1. Air-cooled suits Air systems weigh less than water-cooled systems, tend to keep users dryer, and normally include facial cooling.  Positive pressure inside a suit provides added protection against toxic vapors and alleviates breathing resistance of some respirator systems.  The wearer is attached by an airline to the source of cooled air.
2. Cool vestsA vest with pockets that contain packets of frozen ice packs or PCM gel (phase change material).  Convenient to use and quick to put on.  Requires a refrigerator on site to keep extra packets of frozen ice packs or gel.  The PCM is more comfortable and drier for workers to wear than the traditional ice vest.  The vest may be worn under a full-body impermeable protective suit or on top of work clothing.
3. Water-cooled PPELiquid systems are closed-loop but leaks may be a problem.  They may not be suitable when working around electrical equipment.
4. Reflective suits Aluminized coats, pants, and hoods used for radiant heat protection. When exposed to radiant heat, workers may use garments treated with aluminum.  These reflect up to 90 % of the radiant heat.  When exposed to hot surfaces (greater than 125^oF), workers should wear skin covering to prevent pain or burns on contact-such as thermal gloves.
5. Cool bandanasBandanas filled with a water absorbing material that can be placed on the neck or forehead to help cool. 

Additional recommendations for school sports

1. The factors that put child athletes at risk for dehydration are the same as for adults: Direct sun, prolonged exposure to high temperatures, high humidity, lack of sufficient rest and fluids. The difference is that a child’s body surface area makes up a much more significant proportion of their overall weight than an adult, which means children face a much greater risk of dehydration and heat-related illness than adults do.
2. Dehydration is cumulative (use the dehydration guide).
3. Early dehydration signs include fatigue, thirst, dry lips and tongue, lack of energy, and feeling overheated. However, if a child waits to drink until they feel thirsty, they are already dehydrated.
4. Sports clothing should be light-colored, lightweight and facilitate the evaporation of sweat.
5. Factors that increase the risk of heat illness in children are: A previous episode of dehydration or heat illness; obesity; recent illness (especially if the child has been vomiting or has had diarrhea); and or use of antihistamines or diuretics; a lack of acclimatization and exercising beyond their level of fitness.
6. Move children promptly to cooler (air-conditioned) environments if they feel dizzy, lightheaded or nauseous.
7. Heat exhaustion and heat stroke require immediate medical care. Heatstroke is a medical emergency that, when untreated, can be deadly. Any child with heat stroke must receive immediate medical treatment.
8. For school children additional actions are recommended based on the measured Heat Index value. The recommended risk-based actions is provided in table below.

Recommended risk-based actions for school children based on measured Heat Index value