Determination of Environmental Heat Exposures– Measurement Methods

The Wet Bulb Globe Thermometer (WBGT) should be used to asses environmental heat exposures such as Effective Temperature (ET),Corrected Effective Temperature (CET), or Wet Globe Temperature (WGT), which are then converted to estimated WBGT values. However, when air and vapor impermeable protective clothing is worn, the dry bulb temperature is a more appropriate measurement than the WBGT because impermeable clothing does not transfer humid heat loss, but only dry heat loss.

All-in-all these temperature readings may be used to determine the degree of heat stress the worker is experiencing in the work environment and allow a professional to determine how to best address prevention to heat stress injury.

Measurements should be taken as close to the workers’general work area as possible and taken on an hourly basis, during the hottest portion of each shift.  If a worker moves between two or more areas, the measurements from each additional area should betaken with the same guidelines. Hourly WGBTs should be calculated for the full range of tasks including ALL rest periods. Once calculations are made, an individual environmental factors profile should be made for each hot area to be used as a guide for determining when engineering controls and/or changes in work practices or alternate control methods should be used.

No matter if a worker is performing light, moderate, or heavy work, a metabolic heat screening should be performed. The workers’ heart rate should be recorded to determine if heat exposure is above the recommended exposure limit (REL). If the REL is exceeded, heat production levels should be measured by indirect calorimetry if possible. Although not always feasible to test on-site, REL measurements can also be gathered by monitoring those performing at similar work levels in a controlled setting.

Heat Alert Program

At HFA we believe a huge factor in controlling heat stress is recognizing and predicting conditions that are likely to be dangerous.

A written heat alert program should be developed and implemented in case of heat advisories or heat waves. A heat wave is indicated when the maximum daily temperature is above 95F or when the daily maximum temperature exceeds 90F and is 9 degrees or more above the previous day’s max temperature. The alert program should notify workers and supervisors that conditions greater than the REL are expected and to follow the heat stress plan to adjust operations, break regimens, and hydration intake.

Thermal comfort for warehouses, supply chain distribution facilities and industrial spaces are of particular importance for hot, humid climates.  Space ventilation and conditioning in these environments must be healthy and safe at a minimum with further consideration recommended for additional comfort and productivity enhancing measures.  There are several design strategies that sit between basic OSHA ventilation requirements and full comfort cooling that warrant engineering and economic analysis in order to choose the optimal approach for your facility.

Do you have questions about which cooling option is best for your warehouse or upcoming project?Contact Scott West, P.E. with HFA at 479.273.7780 ext. 528.