Heat Stress

7/6/2020

Make sure we have plenty of water available and if anyone feels a little exhausted or dizzy, let your team lead or fellow employees know and seek some shade and rest.  Heat stress is nothing to fool with.  Every year we hear about unfortunate outcomes of people not taking the proper precautions when working in the sun.

While OSHA does not have any regulation that addresses heat stress, the OSHA web page has lots of information on heat-related illnesses and the importance to institute good work practices and being able to recognize the various signs and symptoms of heat stress. Early signs include:

• headache
• nausea
• dizziness
• weakness
• irritability
• thirst
• and heavy sweating.

The four main heat-related illnesses are: Heat rash, heat cramps, heat exhaustion and heat stroke.  If we ignore the signs and symptoms of the initial stages, we are now susceptible to the life-threatening condition of heat stroke. When this happens, we have lost our internal moisture and therefore, lost the body-cooling mechanism of evaporation.  That means, we are no longer sweating, and our body core temperature now raises to dangerous levels. Once a person reaches this stage, emergency steps such as immediate cooling need to be administered….and that means skipping any decontaminations steps, while someone dials 911 for immediate medical assistance.

While several projects use a device known as a “wet bulb – globe temperature meter” (sometimes referred to as simply a WBGT – pronounced webget), this instrument cannot determine individual responses to elevated temperature exposures. What it does, is take the contributing heat factors of dry bulb temperature (the typical temperature that the weather stations announces), wet bulb temperature (the cooling effects of evaporation) and globe temperature (the radiative effects from the sun light) and combines these three measurements to yield a reading that can then be used to determine a specific work/rest cycle. But these measurements do NOT consider a person’s physical condition as well as the type of clothing worn (many disposable coveralls are impermeable, not allowing for our sweat to leave our skin surface; thereby diminishing the cooling effects of evaporation).

So how can we determine an individual’s susceptibility to extreme heat conditions? As it turns out, a group, other than OSHA, known as the American Conference of Industrial Hygienists or ACGIH, developed a simple assessment method based on a piece of equipment called an Oxypulse meter. This inexpensive device (typically costing less than $50 per unit) is placed on a persons’ index finger while measuring the pulse (it also measures a persons’ blood-oxygen concentration – which should be no less than 95% and is typically around 98%). 

According to ACGIH, by comparing a persons’ heart rate (in beats per minute) to the simple formula of  “180 minus an individual’s age” a body burden can be determined to be either acceptable or requiring an individual to stop work and rest before that person succumbs to a heat-related illness. For instance, a person 40 years of age would have a body burden limit of  “180 – 40 = 140.” Therefore, that person’s heart rate should never exceed 140 bpm. Checking a persons’ heart rate would typically be conducted after 1 hour of field work. A person who exceeds his/her limit would only be allowed to return to their assigned work task once their heart rate drops below 120 bpm (also an ACGIH guideline) and would then only be allowed to work for 2/3 of their previous work period; that would be 40 minutes.

The specific methods that TPMC uses to determine heat stress conditions can be found in the TPMC Corporate S&H Program, “Temperature Extremes” (which is attached in this email).

While no one measurement method can be 100% reliable, having team members work together, observing fellow workers for signs and symptoms of heat stress illness and making sure there is adequate water and/or electrolyte replenishment, taking periodic breaks in a shaded area; are all things we can do to be proactive during heat-stress weather conditions. AND, should you ask a fellow employee how he/she is doing and their response seems to be questionable, it’s OK to tell that person that it is time for a break and take his/her heart rate with an oxy-pulse meter or even through the old fashioned method of physically counting beats for 5 seconds and multiplying by 12; thus 10 beats per 5 seconds equates to 120 bpm.            

An institution or reform movement that is not selfish, must originate in the recognition of some evil that is adding to the sum of human suffering, or diminishing the sum of happiness

Clara Barton (Founder of the American Red Cross)