Heat Stress: Medical Screening and Controls for Hot Work questions for the CHST
CHST Domain 1: Hazard and Risk Identification and Control (K1.22 Working in extreme climates). 5 free questions below. Every answer quotes and links the source document it comes from.
Written lesson
Heat Stress: Medical Screening and Controls for Hot Work, 16 min read. Included with every CHST pass.
This lesson explains how the National Institute for Occupational Safety and Health (NIOSH) frames occupational heat stress: the difference between heat stress and heat strain, which limit applies to which worker, how wet bulb globe temperature (WBGT) is calculated, and which controls come first. These are the points the exam tests and the ones that drive real decisions on a hot job.
Sources covered
- NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106) NIOSH Heat Criteria Document
Guidance documents are quoted from the published edition linked above; they are recommendations, not regulations.
Question 1
A crew member is relining a furnace. The shift has high radiant heat, humid air and heavy lifting. By midmorning the worker's skin is flushed, sweating is heavy and heart rate is high as the body tries to shed stored heat. Which term names what the worker's body is showing?
Show answer and source: NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 91
Answer: D. Heat strain
NIOSH defines heat strain as the body's physiological response that tries to move stored heat back to the environment, which matches the sweating and high heart rate. Heat stress is the thermal environment and workload imposed on the person. Heat exposure is the amount of heat the worker experiences. Heat storage is the buildup of heat, not the response.
On the job
A plant physician at a steel mill reviews two workers after a hot shift on a ladle repair crew. One reports that the furnace area was very hot and humid; the other shows flushed skin, heavy sweating and a fast heart rate. She records the first as a description of heat stress, the environment and workload imposed on the crew, and the second as heat strain, the body's physiological response trying to move stored heat back out.
Study aid, not site-specific safety advice. The official rule controls.
Answer D comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 91(opens cdc.gov in a new tab)“Heat strain is the physiological response to the heat stress that attempts to transfer the stored heat back to the environment [Parsons 2003].”
Question 2
A technician carries a thermometer from an air-conditioned trailer to a hot trench. After about five seconds the reading is still rising, but the crew is waiting. The technician wants to log a dry bulb temperature now. Which action fits NIOSH's thermometer precautions?
Show answer and source: NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 91
Answer: D. Wait until the measurement time exceeds the stabilization time, then log it
NIOSH says the time allowed for measurement must be longer than the time the thermometer needs to stabilize. A reading that is still rising has not stabilized. Averaging with the trailer temperature or logging early gives a false value. A narrower range does not shorten stabilization and could put the trench temperature outside the range.
On the job
A safety coordinator at a foundry carries a dry bulb thermometer from the break room to a spot beside a pouring station. The display is still climbing after a few seconds, so he keeps the instrument in place and does not log anything yet. He records the temperature only after the measurement time has run longer than the time the thermometer needs to stabilize.
Study aid, not site-specific safety advice. The official rule controls.
Answer D comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 91(opens cdc.gov in a new tab)“The time allowed for measurement must be greater than the time required for thermometer stabilization.”
Question 3
During a summer toolbox talk, a laborer on a road crew says he skips fluids the evening before and the morning of a shift. He believes this "toughens" him against heat. The foreman has seen other crew members do the same. According to NIOSH, what should the employer do about this belief?
Show answer and source: NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 40
Answer: B. Counter it through education, because the belief is dangerous
NIOSH's heat criteria document calls the idea of being "hardened" by deliberate dehydration a dangerous misperception that education must counteract. Waiting for symptoms ignores that duty. Acclimatization does not make dehydration acceptable. Drinking extra water later does not make the practice safe, and the belief still needs correcting.
On the job
A site superintendent at a pipeline construction project overhears a welder's helper say that going without water between shifts builds a kind of resistance to summer heat. Rather than shrugging it off as personal preference, the superintendent adds a heat session to the weekly crew meeting. NIOSH calls this belief a dangerous misperception, so the session is meant to counter it through education and replace it with correct fluid practices.
Study aid, not site-specific safety advice. The official rule controls.
Answer B comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 40(opens cdc.gov in a new tab)“A misperception may exist that someone can be “hardened” against the requirement for fluids when exposed to heat by deliberately becoming dehydrated before work on a regular basis. This misperception is dangerous and must be counteracted through educational efforts.”
Question 4
Two roofers on a hot deck are paired as buddies and have both been taught the early signs of heat illness. Midafternoon, one roofer notices his partner is slurring words and walking unsteadily, and says he feels dizzy. The partner insists he only needs to finish the row. What should the buddy do?
Show answer and source: NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 111
Answer: C. Send the partner to the first-aid station for evaluation and possible first-aid treatment
NIOSH's buddy system guidance says a worker showing signs of an impending heat-related illness should be sent to the first-aid station for fuller evaluation and possible treatment. Waiting until the row or shift ends, returning to work after water alone, or resuming work from the shade all skip that evaluation step.
On the job
At a refinery turnaround, two pipefitters work as buddies inside a hot, enclosed exchanger bay. Midshift, one pipefitter sees his partner's face turn flushed and his hands begin to tremble, though the partner says it will pass. The buddy calls the crew's designated medic and walks him to the first-aid station. Under the buddy system, a worker showing signs of impending heat illness is sent there for fuller evaluation and possible first-aid treatment.
Study aid, not site-specific safety advice. The official rule controls.
Answer C comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 111(opens cdc.gov in a new tab)“Any worker who exhibits signs and symptoms of an impending heat-related illness should be sent to the first-aid station for more complete evaluation and possible initiation of first-aid treatment.”
Question 5
A safety coordinator has already given all workers a heat illness course. She is now adding a module just for supervisors. A heat wave is forecast for next week, and supervisors will need to decide whether to change the schedule. Which topic belongs in the supervisor-only module?
Show answer and source: NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 111
Answer: C. How to monitor weather reports
NIOSH says supervisors should receive extra training on implementing acclimatization, procedures when a worker has symptoms including emergency response, and how to monitor weather reports. Weather monitoring fits the forecast heat wave. Rectal core temperature measurement, reviewing private medical records, and choosing vest brands are not on that list.
On the job
A site superintendent on a pipeline crew has a heat-illness orientation behind every worker, then sets aside time for the foremen alone. Part of it covers how to monitor weather reports, so a foreman who sees a hot, humid stretch in the extended forecast can raise it at the planning meeting before the temperature climbs. The same session covers implementing acclimatization and the emergency steps to follow when a worker shows heat-related symptoms.
Study aid, not site-specific safety advice. The official rule controls.
Answer C comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 111(opens cdc.gov in a new tab)“In addition to being trained about each of those topics, supervisors should be trained on the following: (1) How to implement appropriate acclimatization. (2) What procedures to follow when a worker has symptoms consistent with heatrelated illness, including emergency response procedures. (3) How to monitor weather reports.”