ENMT322 Occupational Health and Safety
Week 4 Assignment
Evaluation of Workplace Hazards
Wet-bulb Globe Temperature [WBGT] The Wet Bulb Globe Temperature (WBGT) is a measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). This differs from the heat index, which takes into consideration temperature and humidity and is calculated for shady areas. WBGT measurements are used to determine when heat exposure hazards are present in the workplace. After the WBGT is measured, clothing adjustment factor added, and workload translated into metabolic rate.
For each step, record the information found on the Table located at the end of the lesson. This will be your assignment submittal!
Step 1: Assessing Conditions
Using the link below, perform an evaluation of the heat stress exposure for your “workplace”. (If working from home, use that as your workplace). Be sure to use the information for OUTDOORS. https://www.weather.gov/tsa/wbgt Once you have clicked on the map to reflect your location, record the information on the Answer Sheet found at the end of this lesson.
Step 2: Clothing Adjustment Factors (CAF):
Identify the ACGIH CAF based on the clothing workers are wearing from Table 2. Add the CAF to the WBGT to determine WBGTeff.
Table 2: Clothing Adjustment Factors
Clothing Worn CAF
Work clothes (long sleeves and pants). Examples: Standard cotton shirt and pants 0
Coveralls (w/only underwear underneath). Examples: Cotton or light polyester material 0
Double-layer woven clothing 3
SMS Polypropylene Coveralls 0.5
Polyolefin coveralls. Examples: Micro-porous fabric (e.g. Tyvek suits) 1
Limited-use vapor-barrier coveralls. Examples: Encapsulating suits, whole-body chemical protective suits, firefighter turn-out gear 11
Example:July 2, 2020 @ 4 pm – HAZMAT Responder (firefighter) working a fuel spill outside onHwy 90 in Pensacola, Florida.
WBGT: 84 degrees FWBGTeff = 84 degrees F + 11 degrees = 95 degrees F
Record your information on the Answer Sheet.
Step 3: Determine the Metabolic Work Rate
The ACGIH metabolic work rates represent impacts to the body core temperature from the heat produced internally as exertion increases. Select a work category in Table 3 that best represents the workload using the examples as a guide. If different work activities are planned for the day, use the heaviest workload activity to determine if it’s possible the workers exposure will exceed the allowable limit without controls.
Using the equation below, determine the Estimated Metabolic Rate. Multiply the metabolic rate from the table the ratio of the workers body weight to 70 kg (154 lbs).
Table 3: Metabolic Work Rates
Work Category Metabolic Rate (Watts) Activity Examples Jobs
Rest 115 Sitting Reading a book
Light 180 Sitting, standing, light arm/hand work and occasional walking Bank teller, store cashier
Moderate 300 Normal walking, moderate lifting Retail, food server in restaurant
Heavy 415 Heavy material handling, walking at a fast pace UPS Delivery
Very Heavy 520 Pick and Shovel Work Construction crew
MRest =Work Category (in Watts from Table 3) x worker body weight (in lbs.)
Example: 187 lb male working the HAZMAT spill from Step 2.
MRest = 415 Watts x 187 lbs = 504 W
Record your information on the Answer Sheet
Step 4: Determine the Threshold Limit Value or Action Limit:
The TLV is the temperature at which there is a heat hazard present for an acclimatized worker and the AL is the temperature at which there is a heat hazard present for a non-acclimatized worker. Once these limits are reached, either through environmental factors or workload, controls are necessary to prevent heat-related illness. Controls include work/rest regimens, shade, and hydration.
Using your results from Steps 1, 2 and 3, determine the TLV for an acclimatized worker and an Action Limit for an unacclimatized worker.
a. Convert WBGTeff Farrenheit° to Celsius°
C= ( __°F -32) x 5/9
b. Find WBFTeff on the y-axis and follow it across the table from left to right until it crosses either the dotted line (for AL) or solid line (for TLV) at the appropriate Metabolic Rate on the x-axis.
c. Record your information on the Answer Sheet
Example: HAZMAT Worker from Steps 2 & 3.
WBGTeff = 95°F or 35°C
MRest = 504 WPart B: WBGT Answer Sheet – Record your answers with the proper units (i.e. F, C, %, etc)
(geographic location, place of business, physical description of area where work is taking place)
Forecasted Max Temp(F°)
Relative Humidity (%)
Wind Speed (mph)
Clothing Adjustment Factor
Did your worker exceed the AL?
Did your worker exceed the TLV?
Double check your work:
Did it match your evaluation?
ENMT322 Occupational Health and Safety