Heat Stress

Updated June 29, 2010


Thermal stress is a significant physical agent comprised of degrees along a five-zone continuum.  The comfort zone is in the middle of the continuum.  The middle of the continuum is where most people find thermal conditions to be comfortable, neither hot nor cold and productivity is at its best.  Thermal comfort is also dependant on a number of variables in addition to temperature such as humidity, air movement activity, clothing and individual physiology. 

On either side of the comfort zone you have the heat stress and cold stress discomfort zones.  Within these two zones individuals are able to work safely without experiencing heat or cold stress disorders although productivity and work quality may decrease with an increased risk of accidents.

Signs & Symptoms

The two outer zones of the thermal stress continuum are the health risk zones.  With physiological limits reached and productivity extremely diminished in the health risk zone, the possibilities of heat and cold stress disorders are increased drastically.  In the health risk zone, exposure must be closely managed.

Heat stress

  • fainting (heat syncope)
  • heat rash
  • dehydration
  • heat cramps
  • heat exhaustion
  • heat stroke

Cold stress

  • Reynaud’s disorder
  • chilblain
  • trench foot
  • frostnip
  • frostbite
  • hypothermia

Work procedures

Degree of thermal stress is influenced by three factors, climatic conditions of the environment, clothing and physiological work demands.  The objective for thermal stress evaluations and control is to limit exposure to the comfort zone.

MIT Policy

It is MIT policy to provide a work environment free from recognized hazards causing or likely to cause physical harm.  Thermal stress, hot or cold is one such hazard.  OSHA does not have a special rule for thermal stress although workers are protected under the General Duty Clause of the Occupational Safety and Health Act.

Who to Contact

A thermal stress evaluation can be requested through Environment, Health and Safety by calling (617) 452-EHSS (3477).  Following your request an IHP/EHS representative will contact you by telephone, ask you questions relative to thermal stress and visit your site.  The site visit will consist of athermal stress exposure survey to determine if a threat for thermal stress disorder exists.  If a threat does exist as determined by a combination of factors related to the environment, clothing and workload, technical support and recommendations will be made by the IHP/EHS representative.  Recommendations may consist of administrative controls, training, implementation of engineering controls and personal monitoring.