Posted on

Heat Stress Monitors – Important, Yet Often Overlooked Safety Tools

Sper datalogging WBGT heat stress monitor with datlogging option. P/N 800037

Heat stress is the reaction of the body to working in warm/hot environments – the combined effect of temperature, humidity and radiant heat. Individuals who routinely work in high temperature environments become heat-acclimated and though still subject to heat induced illnesses, are more tolerant of high temperatures.

Heat stress ideally is monitored by measuring core body temperature. This is impractical and based on extensive experimental data, commercial heat stress monitors measure air temperature, humidity and radiant temperature to calculate a Heat Index for indoor and outdoor work environments which is correlated to risk levels. The table below summarizes OSHA’s Heat Index Guidelines. Additional guidance from OSHA’s website can be accessed here.

Summary of Heat-Related Risk Levels and Associated Protective Measures

The most critical actions employers should take to help prevent heat-related illness at each risk level:

Heat Index Risk Level Protective Measures
<91°F

Lower (Caution)
  • Provide drinking water
  • Ensure that adequate medical services are available
  • Plan ahead for times when heat index is higher, including worker heat safety training
  • Encourage workers to wear sunscreen
  • Acclimatize workers

If workers must wear heavy protective clothing, perform strenuous activity or work in the direct sun, additional precautions are recommended to protect workers from heat-related illness.*

91°F to 103°F
Moderate In addition to the steps listed above:

  • Remind workers to drink water often (about 4 cups/hour)**
  • Review heat-related illness topics with workers: how to recognize heat-related illness, how to prevent it, and what to do if someone gets sick
  • Schedule frequent breaks in a cool, shaded area
  • Acclimatize workers
  • Set up buddy system/instruct supervisors to watch workers for signs of heat-related illness

If workers must wear heavy protective clothing, perform strenuous activity or work in the direct sun, additional precautions are recommended to protect workers from heat-related illness.*

  • Schedule activities at a time when the heat index is lower
  • Develop work/rest schedules
  • Monitor workers closely
103°F to 115°F High In addition to the steps listed above:

  • Alert workers of high risk conditions
  • Actively encourage workers to drink plenty of water (about 4 cups/hour)**
  • Limit physical exertion (e.g. use mechanical lifts)
  • Have a knowledgeable person at the worksite who is well-informed about heat-related illness and able to determine appropriate work/rest schedules
  • Establish and enforce work/rest schedules
  • Adjust work activities (e.g., reschedule work, pace/rotate jobs)
  • Use cooling techniques
  • Watch/communicate with workers at all times

When possible, reschedule activities to a time when heat index is lower

>115°F Very High to Extreme Reschedule non-essential activity for days with a reduced heat index or to a time when the heat index is lower

Move essential work tasks to the coolest part of the work shift; consider earlier start times, split shifts, or evening and night shifts.

Strenuous work tasks and those requiring the use of heavy or non-breathable clothing or impermeable chemical protective clothing should not be conducted when the heat index is at or above 115°F.

If essential work must be done, in addition to the steps listed above:

  • Alert workers of extreme heat hazards
  • Establish water drinking schedule (about 4 cups/hour)**
  • Develop and enforce protective work/rest schedules
  • Conduct physiological monitoring (e.g., pulse, temperature, etc)
  • Stop work if essential control methods are inadequate or unavailable.
*The heat index is a simple tool and a useful guide for employers making decisions about protecting workers in hot weather. It does not account for certain conditions that contribute additional risk, such as physical exertion. Consider taking the steps at the next highest risk level to protect workers from the added risks posed by:

  • Working in the direct sun (can add up to 15°F to the heat index value)
  • Wearing heavy clothing or protective gear

**Under most circumstances, fluid intake should not exceed 6 cups per hour or 12 quarts per day. This makes it particularly important to reduce work rates, reschedule work, or enforce work/rest schedules.

Examples of Heat Stress Monitors

Heat stress monitors measure (directly or indirectly) radiant temperature, wet and dry bulb temperature. Older instruments used a 10″ diameter black-body globe for radiant temperature, wet bulb temperature was measured via a wetted thermometer, with water reservoir, and dry bulb temperature using a shaded thermometer protected from air currents.

Most modern heat stress monitors can be hand-held, tripod mounted or permanently situated in a hot work-place. By directly measuring %RH the need for a continuously wetted thermometer and water supply is removed. The former 10″ globe black-body has shrunk to 2″ or 3″.

Examples of small, highly accurate hand held instruments are abundant. Two products SMG represents are shown below along with a wall or desk mounted heat stress monitor. Data logging is common and a convenient way collecting data for analysis of workplace conditions through the work-day.

Examples of Sper Hand Held and Wall/Desk Mounted Heat Stress Monitors
Examples of Sper Hand Held and Wall/Desk Mounted Heat Stress Monitors
Posted on

Prevent Heat Illnesses

Prevent Heat Illnesses

From 1999 to 2013 deaths from heat averaged 1.5/million population annually as reported by the EPA.

The EPA reports heat related deaths averaged 1.5/million population from 1999-2013.
https://www3.epa.gov/climatechange/science/indicators/health-society/heat-deaths.html

Heat illnesses – heat exhaustion, heat cramps and heat stroke can lead to death. These illnesses and deaths are preventable. Heat illness results when the core body temperature exceeds 104F and is evidenced by heat cramps, heat exhaustion and heat stroke. Heat stroke frequently results in death.  Measuremment of core body temperature is intrusive and uncomfortable for workers and not easily done on a routine basis. There is no OSHA standard for work in hot environments which can lead to heat illnesses. Citations for heat illnesses are under the “General Duty Clause”

Work to develop a tool for monitoring conditions leading to heat illnesses was spearheaded by the Navy. The instrument they developed is known as a WBGT heat stress monitor. This  measures wet bulb and dry bulb temperature, ambient temperature and radiant (globe or black body) temperature, hence the acronym WBGT. These values are used to compute an indoor or outdoor WBGT temperature index, from which recommended work/rest cycles are derived by referring to empirically derived charts/tables listing work/rest period frequency and duration.

The latest instruments do not rely on a wetted thermometer for measuring the wet bulb readings to calculate humidity as did the early instruments. They also use a much smaller black body, globe, sensing element for radiant temperature.  Without the wetted bulb, the need for a water tank has been done away with and lengthy measurement periods are routinely done. The elimination of the wet bulb also removed the need for replenishing a water reservoir and the periodic cleaning of the system.

These newer instruments have other advantages including being easily handheld, light weight, many offer on-board datalogging and direct calculation of indoor and outdoor WBGT temperature indexes. The WBGT indexes are used to establish work/rest cycles for heat-acclimated persons under varying work level conditions such as light, medium and high exertion levels. Examples of the latest handheld WBGT heat stress monitors, and a wall mounted WBGT instrument are shown below. Click on any of the instruments for additional information on that instrument.

Sper datalogging WBGT heat stress monitor with datlogging option. P/N 800037
Sper WBGT Heat Stress Monitor with Data Logging Option P/N 800037

Sper Handheld WBGT Heat Stress Monitor, P/N 800036
Sper Handheld WBGT Heat Stress Monitor, P/N 800036

Sper Wall Mount WBGT Heat Stress Monitor with Datalogging option 800034/800035
Sper Wall Mount WBGT Heat Stress Monitor with datalogging option 800034/800035