Heat stress is defined as the net (overall) heat burden on the body from the combination of the body heat generated while working, environmental sources (air temperature, humidity, air movement, radiation from the sun or hot surfaces/sources) and clothing requirements1 . It is obvious to see why heat stress is an issue for employees who work around radiant heat sources or have direct physical contact with hot objects like in iron and steel foundries or outdoor construction work, but is also important for the service sector. For example, workers in bakeries, commercial kitchens, outdoor operations, and laundries may be exposed to heat stress.
It is important to know how the body reacts to heat and the symptoms which may put your health at risk. Age, weight, degree of physical fitness, degree of acclimatization, metabolism, use of alcohol or drugs, and a variety of medical conditions such as hypertension all affect a person's sensitivity to heat, and even the type of clothing worn must be considered3.
The process by which the body can adapt to heat exposure is called acclimatization. After a period of acclimatization, the same activity will produce fewer cardiovascular demands. The worker will sweat more efficiently (causing better evaporative cooling), and thus will more easily be able to maintain normal body temperatures.
Cool (10-15°C) water or any cool liquid (except alcoholic beverages) should be made available to workers to encourage them to drink small amounts frequently (e.g.8 ounces every ½ hour)
Employers need to evaluate their workplaces to ensure workers are protected in hot environments. Elements of a hot environment prevention program include4:
For more information on prevention, check out the OSSA's "Working in Heat" hazard kit: Working in Heat.
|Work Demands||Light||Moderate||Heavy||Very Heavy||Light||Moderate||Heavy||Very Heavy|
|75% work; 25% rest||30.5||28.5||27.5||-||29.0||26.5||24.5||-|
|50% work; 50% rest||31.5||29.5||28.5||27.5||30.0||28.0||26.5||25|
|25% work; 75% rest||32.5||31.0||30.0||29.5||31.0||29.0||28.0||26.5|
* For unacclimatized workers, the permissible heat exposure TLV should be reduced by 2.5°C
Examples of work loads:
Light work -- sitting or standing to control machines, performing light hand or arm work Moderate work -- walking about with moderate lifting and pushing Heavy work -- pick and shovel work, digging
Adopted from: 2001 TLVs and BEIs: Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 2001. p. 171-172.
1 Reference: American Conference of Governmental Industrial Hygienists.
2 Reference: Presentation "Working in Hot Environments" by Leon Genesove, Provincial Physician Ontario Ministry of Labour, OSSA - June 19, 2002
3 U.S. Dept. of Labour, OSHA Technical Manual, Web site: OSHA Technical Manual
4 Reference: Presentation "Working in Hot Environments" by Leon Genesove, Provincial Physician Ontario Ministry of Labour, OSSA - June 19, 2002
5 Source: Canadian Centre for Occupational Health and Safety Web site: CCOHS Physical Agents
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