Working in high temperatures and high humidity for an extended period can result in heat-related illnesses. Implementing a comprehensive heat stress program can have a positive impact on safety and productivity. Ensuring adequate hydration, rest and cooling are part of a heat stress program and help to lower risks for heat stress and other heat-related issues.

A heat-related illness prevention program should include:

1) the individual who will be responsible for ensuring the program is in place (e.g., supervisor, foreman, safety coordinator, crew leader, etc.),

2) the heat-related hazards and workers at risk,

3) ways to protect workers and the resources required (e.g. water, access to a shaded area, etc.),

4) training for workers and supervisors on how to identify, prevent, and respond to heat-related illnesses, and

5) steps for aiding workers suffering from a heat-related illness including emergency preparations for possible heat stroke cases.

Specific actions:

• Check the extended weather forecast. Call or visit the National Weather Service at http://www.weather.gov/ to plan for upcoming work and prior to the start of each workday to ensure that adequate plans are in place to protect workers. You can also receive weather alerts on your cell phone or computer through http://weather.weatherbug.com/?stick=1 or the National Weather Service at http://www.erh.noaa.gov/er/iln/WEA/wireless_emergency_alert.php.
• Conduct worker and supervisor training on how to prevent and identify heat-related illnesses, and provide regular reminders.
• If possible, schedule work activities during cooler times of the day and shade the work area.
• Acclimatize workers to working in a hot work environment. With no recent exposures to heat stress, acclimatization may require up to two weeks of gradually increasing heat stress exposure.
• Make sure all workers know where to go for water and shade. Locate water and shaded areas or air-conditioned areas for breaks as close as practical to where the work is being performed.
• Identify the quantity of drinking water and ice, and the number of disposable cups that will be needed for the shift. Remind workers to drink water and the amount they should drink – OSHA recommends drinking small amounts of water before workers become thirsty or “at least one pint of water per hour in moderately hot conditions… 6 ounces or a medium-sized glass-full every 15 minutes.” Keep water containers in sanitary conditions.
• Increase the frequency of rest and water breaks to prevent dehydration and over-heating during heat waves or days of excessive heat (when the temperature equals or exceeds 95 degrees Fahrenheit).
• Keep a thermometer on the job and check it hourly to ensure that preventative measures are taken if there are unexpected changes in temperature and weather conditions.
• Encourage workers to wear light-colored, loose-fitting, breathable clothing (e.g. cotton), and increase the monitoring of those workers using personal protective equipment (PPE) that covers the body or face.
• Ensure that an emergency response plan is in place and includes: who will respond, steps for handling a worker with a heat-related illness (e.g. who will stay with the person, who knows first-aid, etc.), a map of the site and directions for emergency medical services, and how to address potential language barriers. Heat stroke can pose an imminent threat to life and health, so on remote or difficult to access construction sites the plan should address air evacuation or rapid ambulance access.

Administrative Controls

3M QUESTemp° 46 Heat Stress Monitor

• Monitors: Fahrenheit and Celsius scales, wet bulb, dry bulb, globe, WBGT indoor, WBGT outdoor, relative humidity, heat index, Humidex, air flow
• Weight: 2.6 pounds
• Features: multiple data logging intervals, optional remote sensors for up to (3) simultaneously monitored areas, air velocity sensor, stay time/work rest cycles based on the ACGIH TLV Handbook, rechargeable battery
• Dimensions: 9.2 inches by 7.2 inches by 3 inches

Studies have documented the impact of heat-related illnesses on productivity. According to California’s largest provider of workers compensation insurance, “[r]ecognizing the warning signs and symptoms of heat-related illnesses and using preventive and control measures can reduce the frequency and severity of heat illness while increasing worker productivity (Preventing Heat Related Illnesses)."

Engineering controls are always superior to administrative controls and personal protective equipment, where it is feasible to directly control the hazard. Engineering solutions to consider, especially for low humidity conditions, include down-blast ventilation or fans to increase evaporative cooling, evaporative cooling units for rest stations or stationary work locations, water misting or fogging for rest stations. Semi-portable or permanent air conditioning of vehicle cabs or rest locations may also be feasible, and will be more effective in high humidity conditions.

For very high heat conditions, such as work in impervious protective suits, cooling vests using ice or chilled water may reduce body core temperatures. Where supplied breathing air is provided, cyclones or other devices are available which chill the breathing air or air for positive pressure protective clothing.

Employers should provide training to workers so they understand what heat stress is, how it affects their health and safety, and how it can be limited.

A 2011 study of 37,816 Thai workers examined the relationship between occupational heat stress and kidney disease. After analyzing data from both 2005 and 2009, the study found that more men were exposed to heat stress than women. Men exposed to extended periods of heat stress were 2.22 times more likely to develop kidney disease than those who did not experience such conditions. In addition, men 35 years old and older experienced a 2.2% chance of developing kidney disease when exposed to heat stress while those not exposed experienced a 0.4% chance. Overall, among workers in Thailand’s tropical climates, exposure to heat stress had a direct link to kidney disease (Tawatsupa, 2012).

Although it is universally recognized that maintaining adequate levels of hydration to prevent heat stress is important, many workers and supervisors ignore the facts and continue to demonstrate poor levels of hydration in the work field. Strategies to help promote good hydration are often neglected. Recent studies have shown a consistent pattern of poor hydration in workers employed in industries where environmental heat stress is a common problem. An Australian research study tested workers by administering a urine test during working hours. The results showed that greater than 70% of 710 workers indicated poor hydration, and 51% showed hydration poor enough to put the workers at high risk for heat related illnesses (Miller, 2009).

The American Conference of Governmental Industrial Hygienists (ACGIH) assigned heat a Threshold Limit Value (TLV) based on time-weighted averages (TWA) of Wet-Bulb Globe Temperature (WBGT). WBGTs are not the same as standard temperature readings because they integrate the effect of humidity through a wet bulb reading and radiant heat with a black globe reading. The TLVs are ratios of work to rest needed for different WBGT values. For example, within every hour worked in the cycle, the percentage of time to work during that hour at temperatures at or above the TLV is shown in the first column. WBGT values must be adjusted for the type of clothing worn (ACGIH, 2013). The TLV booklet goes into great detail about heat stress prevention, measurement and control. It can be purchased at: http://www.acgih.org/store/.

Eileen Betit - CPWR - The Center for Construction Research and Training.  Dan Anton, PT, PhD, ATC – Eastern Washington University.  Andrew Kingston, Michael R. Cooper and Bruce Lippy – The Lippy Group

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