In the General Industry Standard 29 CFR 1910.132, Personal Protective Equipment (PPE), OSHA requires employers to assess workplace hazards which necessitate the use of PPE. If hazards are present, employers are required to select PPE that will protect employees. Paragraph (c) requires that the PPE be of safe design and construction for the work to be performed. Also, paragraph (f)(1)(iv) requires training to include the limitations of the PPE. The focus of this paper is to identify PPE available to assist in preventing heat stress, paragraph (c) safe design and construction, and paragraph (f) limitations. As safety and health professionals we have to determine if the control we select, in this case PPE, introduces other hazards (limitations, safe design and construction). Use of certain types of PPE may impact the potential for heat stress disorders. Use of certain types of PPE is offered as protection when heat stress is an identified hazard. As a result, we have both a control and a limitation.
Let's first address PPE that is marketed as a control or preventive measure for heat stress. Some PPE products are for very specialized applications and others are offered as a more general control. Some of the specialized applications include protection for fire fighters, welders, and other hot applications requiring temperature resistance. We'll narrow the focus here to deal with PPE offered as a general control to manage and prevent heat stress. We will also limit our discussion by not including sun protection.
Before we review PPE, let's first summarize the physiological response to reduce the increased heat load on the body. The primary cooling actions that occur include:
Increase blood flow to the skin for heat dissipation;
Increase sweating; and
Increased heart rate to move the blood and heat to the skin.
These actions occur to prevent a rise in the core body temperature. The hypothalamus works to keep core body temperature at 37°C ± 1. Normal body temperature taken rectally is 37.6 °C (99.6 °F), or taken orally 37 °C (98.6 °F). Programs to prevent heat stress illness should attempt to prevent a rise in core body temperature above 38 °C (100.4 °F). That is less than 1 °C!
An expert panel for the world Health Organization (WHO) recommends a peak value of 39 °C (102.2 °F) under closely monitored conditions. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a peak of 38.5 °C (101.1 °F) to allow a margin of safety.
The body relies on radiation (heat transfer via waves) and evaporation (heat is transformed from a liquid to a vapor) for heat loss in hot environments. As long as the air temperature remains less than body temperature, approximately 65% of the body's heat loss occurs by radiation. If air temperature exceeds 95 °F radiation of heat basically stops and the body is almost totally reliant on evaporation for heat loss. Evaporation accounts for approximately 30% of the body's heat loss.
