Practical Aspects of an Employer Heat Stress Risk Reduction Process with a Focus on Risk Assessment/Hazard Recognition

With hotter temperatures and longer, more frequent heat waves because of climate change, along with OSHA’s recently announced National Emphasis Program (NEP), employers should be taking practical measures to address the risk of heat-related illnesses as well as be prepared for an OSHA inspection that considers heat hazard exposures to employees. OSHA is currently working on a new standard for heat hazards that is expected to mirror the existing NEP.

A written Heat Stress Management Program will identify the management person(s) responsible for implementation. It will have in place the information and training elements (hourly as well as supervisory) of a typical safety and health program, keeping in mind the languages understood by the employees, with an emphasis on teaching everyone how to recognize the signs and symptoms of heat exhaustion, heat stroke and other heat-related effects on the body, as well as how to protect themselves from the adverse health effects of heat exposure (e.g., drinking cool water throughout their shift, resting in a cool, shady place, etc.). 

The Heat Stress Management Program should identify employees and employee groups most at risk of heat stress. The key factors to consider are level of work activity (light, moderate, strenuous – see the examples listed below), area of the plant or work site (based on such factors as availability of shade, air movement, and heat generating equipment), and the level of acclimatization of individual workers (described further below). 

Finally, the risk assessment and control elements described in more detail below should also be covered by the written program in a way that is easy to understand by all.

Heat Stress Hazard Recognition

NWS Warnings, Alerts and Advisories

The OSHA CPL 03-00-024 that outlines the NEP references the National Weather Service’s (NWS) warnings, alerts, and advisories. These are particularly useful for outdoor worksites but can also trigger your WBGT monitoring plan for more accurate assessment. There are 5 different warnings that employers can take different approaches to address:

The wet-bulb globe temperature (WBGT) is a type of apparent temperature used to estimate the effect of temperature, humidity, wind speed, and visible and infrared radiation (usually sunlight) on humans. It is used by industrial hygienists, athletes, sporting events and the military to determine appropriate exposure levels to high temperatures. It is derived from the following formula:

WBGT = 0.7Tw + 0.2Tg + 0.1Td

Where:

• Tw = Natural wet-bulb temperature (combined with dry-bulb temperature indicates humidity)
• Tg = Globe thermometer temperature (measured with a globe thermometer)
• Td = Dry-bulb temperature (actual air temperature)

1. Excessive Heat Outlook: this is a prediction of an excessive heat event in the next 3-7 days.
   • Identify employee groups most at risk. 
   • Plan to begin WBGT monitoring.
2. Excessive Heat Watch: when conditions are favorable for excessive heat in the next 24-72 hours.
   • Plan to begin WBGT monitoring.
   • Consider what measures to take to protect employees, such as having cool water readily available, and adjusting work schedules to have more work in the cooler hours or to accommodate more frequent breaks.
3. Heat Wave: this is a forecast that is given when the daily high temperature is 95°F or higher or when the daily high exceeds 90°F and is 9°F higher than the preceding days.
   • Begin WBGT monitoring.
   • Begin to implement measures to reduce exposure to those employees most likely to be impacted.
4. Heat Advisory: the maximum heat index (calculation based on temperature and relative humidity/dew point – calculator here: https://www.wpc.ncep.noaa.gov/html/heatindex.shtml) is expected to be 100°F or higher for at least 2 days and the nighttime temperatures will not drop below 75°F.
   • Increase the frequency and duration of breaks in a cool place.
   • Monitor the employees to make sure they are not beginning to experience the first signs of heat stress e.g., dizziness, lightheadedness, nausea, headache.
5. Excessive Heat Warning: this is considered extremely dangerous heat conditions. The maximum heat index is expected to be 105°F or higher for at least 2 days and the nighttime temperatures will not drop below 75°F.
   • Increase the frequency and duration of breaks in a cool place.
   • Reduce the intensity of the work (see metabolic rate categories below).
   • Monitor the employees to make sure they are not beginning to experience the first signs of heat stress, e.g., dizziness, lightheadedness, nausea, headache.

WBGT Monitoring

Wet Bulb Globe Temperature (WBGT) is measured using a WBGT monitor. A WBGT monitor is a measurement tool that uses ambient temperature, relative humidity, wind, and solar radiation from the sun. Measuring WBGT is the most accurate way to assess heat stress and is the basis for the most comprehensive exposure limits, developed over decades by the American Conference of Governmental Industrial Hygienists – ACGIH. There are a number of these instruments available in the marketplace, several of which are less than $500. 

An effective monitoring program will describe the employer’s policy for when and how often in the workday to measure WBGT. NIOSH recommends taking environmental heat measurements at least hourly, during the hottest portion of each work shift, during the hottest months of the year, and when a heat wave occurs or is predicted.

WBGT Exposure Screening and Work/Rest Schedules

The following table is adapted from the 2017 ACGIH TLV (Threshold Limit Value) as a Screening Criteria tool. Use this to incorporate sufficient rest periods in a cool, shady place during excessive heat periods. These guidelines assume cotton work clothes (long sleeves and pants). The WBGT values are reduced if employees are required to wear heavier clothing or vapor-barrier coveralls. WBGT values in °F. 

For acclimated workers, assuming an 8-hr workday in a 5-day work week.

Allocation of rest minutes each hour	Light Work*	Moderate Work	Heavy Work	Very Heavy Work
0 – 15 minutes	88.0	82.0	–	–
15 – 30 minutes	88.0	84.0	81.5	–
30 – 45 minutes	90.0	86.0	84.0	82.0
> 45 minutes	90.5	88.5	86.5	86.0

For non-acclimated workers

Allocation of rest minutes each hour	Light Work	Moderate Work	Heavy Work	Very Heavy Work
0 – 15 minutes	84.0	87.0	–	–
15 – 30 minutes	84.5	79.0	75.0	–
30 – 45 minutes	84.5	81.0	77.5	75.5
> 45 minutes	86.0	84.0	84.0	81.0

*Metabolic Rate Categories

Category	Metabolic Rate (W)	Examples
Rest	115	Sitting
Light	180	Sitting with light manual work with hands and arms
Moderate	300	Sustained moderate hand and arm work, moderate arm, leg work and trunk work. Light pushing/pulling. Normal walking
Heavy	415	Intense arm and trunk work: carrying, shoveling, sawing, pushing/pulling heavy loads; walking at a fast pace
Very Heavy	520	Very intense activity at fast to maximum pace. Pick and shovel work, lifting and carrying heavy weights, shoveling wet sand.

The Heat Stress and Strain TLV (threshold limit value)

While the TLV below is based on the ability of most healthy people to sustain heat stress exposure, cases of heat stroke and other exertional heat illnesses do occur below the TLV. A comprehensive Heat Stress Program and early recognition of symptoms is necessary to prevent heat stress illnesses. The goal of the TLV is to maintain body core temperature to within 1°F of 98.6°F (the normal average for a healthy person. Note that the broken line “Action Limit” is for individuals that have not been acclimatized (more on acclimatization below). It should really be considered a TLV for those individuals whose body has not yet acclimated to the hot work environment.

Acclimatization

This is a gradual physiological adaptation that improves an individual’s ability to tolerate heat stress. Workers who have not been acclimatized are at significantly increased risk of adverse health effects when exposed to heat stress conditions, particularly when placed with other workers who have already been acclimatized. 

Acclimatization requires physical activity under heat stress conditions similar to those anticipated for the work environment. With a history of heat stress exposures of a least two continuous hours for 5 of 7 days (or 10 of 14 days), a worker can be considered acclimatized. However, loss of acclimatization begins when the work under heat stress conditions is discontinued. A loss is noticeable after 4 days and may be completely lost in 3 weeks. This means that a return of summer conditions after winter requires even seasoned employees to re-acclimate to heat conditions.

A practical approach for employers to take regarding acclimatization would be for new workers or workers who have been away from the workplace for 4 or more days to be segregated from fully acclimatized workers and to provide lower intensity work with more frequent breaks for 2 or 3 days while at the same time monitoring them for any of the signs and symptoms discussed above (light headedness, fatigue, headaches).

Guidelines for Assessing Signs of Heat Stress

There are other techniques to consider in combination with monitoring WBGT, specifically, monitoring heat strain signs and symptoms that are considered sound industrial hygiene practices, particularly when clothing may significantly reduce heat loss in the worker.

• Monitor the workers’ heart rate: when sustained heart rate is in excess of 180 bpm (beats per minute) minus the worker’s age (e.g., for a 40-year old worker, this would be 180-40 = 140 bpm), indicates excessive heat strain and the individual should be removed immediately from exposure. Inexpensive heart rate monitors – commonly used by athletes – can be worn on the wrist like a watch.
• Monitor the workers’ core body temperature: when an acclimatized and medically fit worker’s core body temperature is greater than 101.3°F, or a non-acclimatized worker’s core is greater than 100.4°F, they have reached the danger zone and should be removed to rest in a cool place. There are inexpensive core body temperature monitors that measure skin temperature with arm or chest straps, but these are not very accurate for the work environment. The best technique in the work environment is a monitor (e.g., TSI QUESTemp II) in which the sensor is placed in the ear canal like an ear bud.
• When the worker experiences sudden and severe fatigue, nausea, dizziness, or lightheadedness, these are strong indicators of heat stress. However, the individual’s judgment may be clouded by these symptoms and so this technique may be unreliable for some workers.
• A person may be at greater risk of heat-related disorders if profuse sweating is sustained over a period of hours.

Emergency Response

If a worker in a hot work environment ever appears to be disoriented, confused, or irritable, he/she should be removed immediately to a cool location with circulating air and kept under skilled observation. If symptoms persist or get worse, they should be immediately transported to a hospital. To support management and supervisory personnel in the rapid identification of potential heat illness, require the download of the OSHA NIOSH Heat Safety Tool app to their smartphone. This app assists in identifying potential precautions based on the temperature for the location and includes tabs for signs and symptoms and first aid.

Elements to Control Exposure Heat Stress

• Encourage drinking small volumes of cool water about every 20 minutes.
• Encourage employees to report symptoms to a supervisor.
• Encourage co-worker observation to detect signs and symptoms.
• Counsel and monitor workers who take medications that may compromise normal cardiovascular, blood pressure, renal or sweat gland functions and those who abuse or are recovering from alcohol abuse.
• Consider engineering controls that reduce the metabolic rate, provide general air movement and reduce process heat and water vapor release, shield radiant heat sources.
• Consider administrative controls that set acceptable exposure times, allow sufficient recovery and limit physiological strain.
• Consider PPE such as cooling vests. Cooling bandanas can also have a positive effect.

Tags: Hazard Recognition, Heat Stress, Risk Assessment, Risk Reduction