Heat & Cold Stress

For Outdoor Workers: OSHA Heat Index, and Protective Measures

Neither federal OSHA nor MNOSHA have a specific standard that covers working in outdoor hot environments. Nonetheless, under the OSH Act, employers have a duty to protect workers from recognized serious hazards in the workplace, including outdoor heat-related hazards. The following guides will help employers and worksite supervisors prepare and implement hot weather plans.

Using the OSHA Heat Index to Protect Workers

Protective Measures to Take at each Heat Index Risk Level

NIOSH Smartphone Heat Safety App: This free app allows workers and supervisors to calculate the heat index for their worksite, and, based on the heat index, displays a risk level to outdoor workers.

MN Enforcement Guidelines for Outdoor Exposure to Heat Stress

What is Heat Stress?

Heat stress results from a combination of internal heat production from doing work and external heat exposure from the environment. Both aspects need to be addressed properly to control heat stress.
Indoors/Equipment. Heat stress may occur year-round in areas with heat-producing equipment, such as in foundries, kitchens or laundries.
Outdoors. In Minnesota, high temperature and humidity are common during the summer, with daily temperatures routinely varying up to 30 degrees. This variation does not always allow people to become acclimatized and stay acclimatized, thereby increasing the risk of heat stress.

Heat Cramps; Heat Exhaustion; Heat Stroke

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

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.

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.

MNOSHA Indoor Heat Stress Regulations

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.

Table 1. Two-hour time-weighted average permissible heat exposure limits: