Each year we hear of several occurrences of heat stress illness. Some are personal experience, some from local news, and some that make national headlines. The shame of it all is that in most cases, WE ALL KNOW, heat stress illness is preventable. We tend to focus on just a few aspects of heat stress illness management. There is more than enough data and tools available to establish a comprehensive management strategy to prevent heat stress illness from occurring. This management strategy can be prepared and delivered without expensive or sophisticated equipment. This presentation will focus on just such a strategy. It will discuss management in 3 phases:
Training and (early) recognition
Management of personal factors
Understanding and using evaluation tools (including measurement instruments)
Training and recognition should be a basic review for most of us. Early recognition is key since heat stress illness generally occurs in a progression. Early recognition of symptoms and intervention will prevent progression to more dangerous phases.
Before we review signs and symptoms to help us recognize heat related illness may be occurring, 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 of heat stress illness control 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.
NIOSH and OSHA agree on the basic descriptions of heat-related illnesses. For discussion purposes, we will use these to refresh and to determine and focus our management activities. They are listed in order of severity. As we discussed previously, early recognition keeps heat-related illness from progressing to a more dangerous, level.
Heat fatigue - temporary discomfort and mental or psychological strain. Results, to varying degrees, include a decline in task performance, coordination, alertness, and vigilance.
Heat rash - (also known as prickly heat) occurs most often in hot humid environments where sweat is not readily evaporating from the skin and the skin remains wet. The sweat ducts become plugged which results in a skin rash. This appears as red papules. Since the cause is the wetted skin, in dry environments where evaporation is occurring more readily, this may not occur.