Heat illness: what NIOSH, OSHA, CCOHS and WorkSafeBC list
How four official sources name the heat illnesses, the factors behind them and the employer measures they list. No first aid steps are repeated here.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the official source says. It is not legal advice: ask the office named here. It is not medical advice and gives no first aid steps: the agencies' own pages cover those. The sources are general workplace pages, not written for tree work. The rules by place are on heat rules for outdoor work, and the matching page for winter is cold at work.
Four sources side by side
| Source | Illnesses it names |
|---|---|
| NIOSH, heat stress page (March 3, 2026) | Heat stroke, heat exhaustion, rhabdomyolysis, heat cramps, heat rashes. |
| OSHA, heat overview | Heat exhaustion and heat stroke, plus thirst, irritability, a rash and cramping as symptoms of poor heat loss. |
| CCOHS, hot environments | Heat edema, heat rashes, heat cramps, heat exhaustion, heat syncope, heat stroke. |
| WorkSafeBC, heat stress | Heat exhaustion and heat stroke. |
NIOSH
NIOSH publishes a heat stress page that lists these risk factors: high temperature and humidity, direct sun, indoor radiant heat, limited air movement, lack of acclimatization, dehydration, physical exertion, protective equipment and clothing, physical condition and health problems, certain medications, advanced age, pregnancy and a previous heat-related illness. Under employer action it names engineering controls, administrative (work practice) controls and training on what heat stress is, how it affects health and safety, and how to prevent it.
OSHA
The US Occupational Safety and Health Administration says in its heat overview that illness from heat exposure is preventable, yet every year thousands of workers get sick from it and some cases are fatal. It names landscaping and construction among outdoor industries where workers have suffered heat illness. It describes heat dissipation: the body sheds heat by sweating and by sending more blood to the skin, and when that does not happen fast enough, internal temperature keeps rising. It calls heat stroke the most severe heat-related illness. The page also points to a national emphasis program on outdoor and indoor heat hazards, directive CPL 03-00-024, dated April 10, 2026.
CCOHS
The Canadian Centre for Occupational Health and Safety page Hot Environments, Health Effects names the widest list of illnesses of the four: heat edema (swelling, most noticeable at the ankles, in people not used to working in heat), heat rashes, heat cramps, heat exhaustion, heat syncope and heat stroke. It says there are two kinds of heat stroke, one with little or no sweating and an exertional kind where sweating is usually present, and that sweating is not a good sign of heat stress. It says personal protective equipment such as coveralls, safety boots, hoods and gloves can hold in heat and moisture, and that heavy PPE adds physical effort.
WorkSafeBC
The regulator's heat stress page says heat stress happens when the body heats up faster than it cools down, and that all employers are responsible for managing it. It sorts causes into the environment (sun, reflected heat, humidity), the work (active work makes more body heat) and the worker (health conditions, hydration, protective clothing). It names four ways to measure the risk: the Humidex method, the wet bulb globe thermometer method, body temperature and heart rate. It says monitoring should start as temperatures approach 23 to 25 degrees C, and that these figures are not exposure limits, because heat stress can occur at lower temperatures when workers wear protective clothing. Its control list runs from cancelling or postponing the work through shade structures, work-rest cycles, acclimatizing workers, cool water and buddy check-ins.