Heat stress results from a combination of (1) internal body heat production from doing work and (2) external heat exposure from the environment. Both aspects need to be addressed properly to control heat stress.
Cold stress results from being exposed to extreme cold or working in cold environments.
Additional Considerations:
- Heat and cold stress can occur indoors from heat/cold-producing equipment, such as in foundries, laundries, or kitchens (which can have both heat and cold-producing environments).
- It is important to recognize that what constitutes heat or cold stress. Its effects can vary seasonally or even daily, and can vary among individuals.
- This variation does not always allow people to become acclimatized and stay acclimatized, thereby increasing the risk of heat or cold stress.
- Temperature tolerance can be impacted by hydration, overall health, medications, and level of acclimation.
Below are two options to determine how long a person can work in a hot environment, and how long the rest break should be.
Option 1: Use the NIOSH Heat Stress Work/Rest Schedule.
- Note: You must incorporate the temperature adjustments on page 2 of the schedule to account for sunshine and humidity levels.
- The NIOSH Schedule:
- Is based on local air temperature, with adjustments for direct sunlight and humidity..
- Is not as accurate as using the WBGT (which takes measurements in the exact work/field site).
Option 2: Use the WBGT Work/Rest Schedule found in this table. The table is based on the following considerations:
- The Wet Bulb Globe Temperature.
- The type of work (light, moderate, heavy).
- If the person is acclimatized or not to the conditions.
- Water consumption per hour.
- The work/rest cycle per hour.
- If you do not have a WBGT then use this OSHA Outdoor WBGT Calculator for a good approximation (St. Olaf latitude = 44.46; longitiude = 93.16).
Heat Cramps
Prolonged exercise in hot environments may lead to involuntary spasms or cramping in muscles. These are usually more intense and prolonged than a typical leg cramp. It is most common for muscles in your calves, arms, abdomen, or back to be affected but heat cramps may occur in any muscle group that is being utilized during your activity.
How to Respond:
- Rest and allow your body to cool down
- Hydrate and consider having some juice or a sports drink
- Gently massage and stretch the cramping muscles
- Avoid strenuous activity for several hours
- Contact your doctor if the cramps do not go away after an hour
Read more: https://www.mayoclinic.org/first-aid/first-aid-heat-cramps/basics/art-20056669
Heat Exhaustion
Heat exhaustion is a result of your body becoming overheated due to prolonged exposure to high temperatures. This may be compounded by strenuous physical activity (such as fieldwork) and high air humidity.
Symptoms Include:
- Heavy sweating
- Rapid but weak pulse
- Skin that feels cold, pale, and clammy to the touch
- Muscle cramps
- Weakness or fatigue
- Headache and/or dizziness
How to Respond:
Move the person to a cool place (shade, air conditioned vehicle, nearby building, etc.) and take steps to cool them with wet clothes. Apply wet clothes or ice packs to areas of the body with major arteries such as the neck and armpits. This will speed the cooling of the core body temperature.
It is possible that the victim may lose consciousness. If they do, continue to monitor their breathing and heart rate closely and continue efforts to cool them. If symptoms persist for longer than 1 hour, conditions worsen, or the victim is throwing up, contact emergency medical services. Untreated, heat exhaustion may lead to heat stroke which is an immediate medical emergency.
Read more: https://www.mayoclinic.org/diseases-conditions/heat-exhaustion/symptoms-causes/syc-20373250
Heat Stroke
Heat stroke is the most severe heat illness and is specifically characterized by a body temperature that exceeds 103°F/40°C. If left untreated, heat stroke can damage critical organs such as the brain, heart, and kidneys, and in extreme cases may lead to death. Sudden exposure to hot weather, such as traveling to a hotter climate to conduct fieldwork, can increase the risk of heat stroke. Certain health conditions and medications may also increase your risk so always start slow and evaluate how you (and your team) are responding to the environment.
Symptoms Include:
- Hot, red skin. May be damp or dry to the touch
- Fast, strong pulse
- Confusion and/or slurred speech
- Headache and/or dizziness
- Nausea
How to Respond:
Call 9-1-1 immediately. Heat stroke is a medical emergency. After contacting emergency services, move the person to a cooler place (shade, air conditioned vehicle, nearby building, etc.) and take steps to cool them by applying damp clothes. If possible, place them in an ice-bath but be sure to monitor their condition closely and be prepared to support their body.
It is possible that the victim may lose consciousness. If they do, continue to monitor their breathing and heart rate closely and continue efforts to cool them.
If the person starts to vomit, place them in the recovery position to avoid a choking hazard. In the case of heat stroke, you do NOT want to give the person anything to drink because it may induce vomiting or the person may not be able to swallow properly.
Read more: https://www.mayoclinic.org/diseases-conditions/heat-stroke/symptoms-causes/syc-20353581
Heat Index vs Wet Bulb Globe Temperature (WBGT)
- The Heat Index gives only a quick “feel” of the outside environment.
- It based on only two factors: the air temperature and the relative humidity.
- It is measured in the shade, and combines air temperature and relative humidity to represent how hot the conditions feel at rest. The heat index does not account for the effects of wind, sunlight, radiant heat sources, or workload.
- The Wet Bulb Globe Temperature (WBGT) is the core tool used by occupational health professionals because it measures all four factors that contribute to heat stress in workers:
- Ambient air temperature.
- Humidity (high relative humidity makes it difficult for the body to cool itself through sweating).
- Radiant heat from sunlight or artificial heat sources such as furnaces.
- Air movement (in most situations, wind helps workers cool off).
While local weather reports (= heat index) can be useful, the readings from these stations may not reflect the conditions at the specific worksite (or playing field, etc.). Weather reports can be inaccurate if the specific work/field site has features that affect heat conditions. These features include:
- Indoor work — a weather report cannot gauge conditions inside a building.
- Direct sunlight — weather services measure temperature and Heat Index in the shade. Work in the sun may be considerably hotter. Direct sunlight can increase Heat Index by up to 13.5°F (7.5°C).
- Heat sources — weather reports cannot account for the heat generated by fires, hot tar or other materials, ovens, or other hot equipment, or heat-absorbing surfaces such as roads and roof surfaces.
- Wind blockage — some worksites may be hotter than surrounding areas because of structures that block air movement. Examples include trenches, and bowl-shaped athletic stadiums, and the leeward side of buildings (especially if in direct sunlight).
- Reflective material — water, metal, or other materials can reflect sunlight onto workers.
MNOSHA Enforcement Guidelines for Exposure to Heat Stress
• MNOSHA Compliance: Heat Stress
• Outdoor Work: MNOSHA Enforcement Guidelines for Outdoor Exposure to Heat Stress
• Indoor Work: MNOSHA Indoor Temperature Requirements
- Minnesota Rules 5205.0110, subp. 2, is the Minnesota OSHA standard for heat exposure. The standard is based on wet bulb globe temperature (WBGT) and level of work activity.
- Employees shall not be exposed to indoor environmental heat conditions in excess of the values listed in Table 1. The values in Table 1 apply to fully clothed acclimatized workers.
- Employees with exposure to heat shall be provided training according to Minnesota Rules 5206.0700, subparts 1 and 3. Minnesota Rules 5206.1100 (“Labeling Harmful Physical Agents; Label Content”) also apply.
Table 1. Two-hour time-weighted average permissible heat exposure limits: |
|
| Work Activity | WBGT, °F |
| Heavy Work | 77 |
| Moderate Work | 80 |
| Light Work | 86 |
NIOSH Heat Stress Homepage
NIOSH Heat Stress Homepage: Information for workers who are exposed to extreme heat or work in hot environments.
OSHA Cold Stress Guide. Anyone working in a cold environment may be at risk of cold stress. This guide contains frequently asked questions that will help workers understand what cold stress is, how it may affect their health and safety, and how it can be prevented.
NIOSH Cold Stress Homepage: Information for workers who are exposed to extreme cold or work in cold environments.
Minnesota Rules for Minimum Indoor Temperatures:
- Indoor places of employment shall maintain a minimum air temperature of 60°F where heavy work is performed, unless prohibited by process requirements.
- Indoor places of employment shall maintain a minimum air temperature of 65°F where light to moderate work is performed, unless prohibited by process requirements.