Managing The Heat In Florida Workplaces

An Employer's Guide For Developing A Heat Stress Prevention Plan

by Kris Bancroft
Senior Analyst

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This booklet is designed to provide a limited amount of information to employers who manage work in hot environments. If your workers are exposed to hot environments, it is your responsibility to ensure they are not injured by the heat. In the State of Florida, the Division of Safety offers assistance to employers in developing a Heat Stress Prevention Plan. Free consultation in this and other workplace safety and health issues can be obtained by contacting the Division at 1(800) 367-4378

Our individual ability to withstand heat can be reduced by our health and physical conditioning, the equipment we use, changes in our working environment, and day-to-day variables such as caloric, fat, and water intake. Employers and supervisors must know the indicators of higher susceptibility to heat stress.

Dense or impermeable clothing prevents the efficient operation of our body's cooling system. Sometimes, it is necessary to monitor each worker's body heat.

Medicines and medical conditions can cause us to become more susceptible to heat stress. If you are a supervisor, know the medical history and current health of your workers--make allowances for change. If you are an employee, inform your employer when your personal conditions change--don't risk your health or the safety of your co-workers.

As we get older, our body works with less efficiency, making it increasingly difficult for us to endure heat.

Consuming large or heavy meals during (or before), work can significantly increase your susceptibility to heat stress injury.

There are six levels of heat stress. However, they most often do not occur in direct progression. In other words, a worker may suffer heat syncope (fainting) without showing any signs of miliaria (prickly heat.) The manifestation of heat injury following an episode of syncope could well be heat stroke, and the victim could very well never show signs of tetany or edema.

The six kinds of heat stress are:

Prickly Heat

Prickly Heat (a.k.a. "miliaria" or heat rash) is the first manifestation of a heat stress problem. Effective treatment for prickly heat - good hygiene, zinc oxide, talcum powder, corn starch, and changes of clothing or equipment wetted with perspiration.

Heat Fatigue

Heat Fatigue, the second warning of a heat stress problem. Heat fatigue impairs our thought processes and causes us to make mistakes. Sometimes those mistakes are FATAL. Learn to recognize the onset of heat fatigue. Take immediate steps to keep heat fatigue from causing an accident in YOUR workplace. NEVER allow a worker suffering from heat stress to leave work alone, or to be left unattended, unless a physician has evaluated them and says it's OK.

Heat collapse

(a.k.a. "heat fainting" or "syncope") is the third level of heat stress. This condition marks the boundary of some very dangerous territory. When responding to a worker who has suffered from a heat faint, make sure they have not been injured from the subsequent fall.

Standard procedures for responding to and obtaining treatment for heat stress victims suffering from conditions other than simple miliaria.

SENTINEL EVENTS - those which ALWAYS constitute a medical emergency and often permanently impair our ability to function in a hot environment.

In cases of heat tetany, heat edema, or heat stroke, the employer should require the affected worker to obtain a medical evaluation and clearance before returning to work, regardless of whether or not the victim considers it necessary.

Heat Tetany

Heat Tetany, the fourth level of heat stress, is sometimes recognized by the onset of cramping muscles - but not always.

Tetany can be FATAL!

Loss of consciousness ALWAYS constitutes a medical emergency, and the worker who loses consciousness should be evaluated by a medical professional prior to returning to work.

Heat edema

Heat edema, the fifth level of heat stress, and a condition that can be fatal, is an important reason why those workers who suffer from sentinel heat events must ALWAYS receive an immediate medical evaluation.

Heat stroke

Heat stroke, the sixth level of heat stress, is a KNOWN KILLER, and ALWAYS constitutes a medical emergency of the highest magnitude.

for the victim of heat stroke! Heat stroke occurs when the body's cooling system completely shuts down. Look for:

Use a heat index chart as a guide for determining the level of work that can be safely performed in your workplace.

Include heat stress disorders when developing your Comprehensive Emergency Action Plan.


Components of the Comprehensive Emergency Action Plan

CEAP should include:

When it comes to developing an effective CEAP, bigger is not necessarily better. Make an assessment of your workplace. If it is possible that an employee might at some point suffer heat stress, a Heat Stress Prevention Plan is a necessary component for your CEAP.

Determine the needs and options for your workplace that will enable you to prevent a heat stress episode. Two areas of consideration include:

An ample supply of water calculates to about 1_ gallons per person per day. Not only must there be appropriate quantities, drinking water must be readily available for all workers.

Do not increase the amount of salt intake unless you are advised to do so by your physician.

Sometimes the nature of the work requires the employer to provide specialized equipment to protect the employee from the heat associated with doing the work. This equipment must be kept clean and in good working order.

Use the "Buddy" system

Protect the workers from heat source burns. Protective clothing is the standard, but barriers may also be an option.

Remember that a worker's tolerance to hot conditions changes from day to day.

Advise employees to eat lighter meals both before and during work shifts in hot environments. Heavy foods, especially in large quantities, tax the body's cooling system.

The employer is responsible for the health and well-being of the employee, insofar as job safety and health are concerned. Screening applicants with respect to their ability to function in the conditions expected in the workplace should be a standard practice.

The employer should monitor changes in the health of current employees to ensure they are continually fit to work at their assigned tasks. When major health events occur, a clearance from a physician should be obtained prior to the employee's return to work.

Whenever possible, schedule the hottest work or more difficult tasks for the coolest time of the year or the coolest part of the work shift.

Air movement across the skin helps evaporate perspiration and cool the body. When the heat index is below 99 degrees F, a fan can enhance the evaporation rate and makes for an inexpensive means to reduce heat stress in the workplace. However, at temperatures above the 99 degree F threshold, air movement can make the effects of heat even worse.

When the heat index ranges from 90 - 104 F, heat tetany and edema are possible.

When the heat index ranges from 105 - 130 F, heat tetany and edema are probable and heat stroke is possible.

When the heat index rises above 130 F, heat stroke is probable, and this constitutes an UNSAFE working environment.

Advise employees to wear clothing that is suited for the work. Unless heavy/protective clothing is required, wear light weight and loosely woven cotton and cotton blends in hot work environments.

For help in designing and implementing a Heat Stress Prevention Plan, call 1 (800) 367-4378, for a referral to the Division of Safety District Office nearest you.

Designing a Heat Stress Prevention Plan

begins with an assessment of the workplace and the tasks performed by each individual employee in the workplace. Some of the questions the employer should answer include:

Monitor the Workplace and Determine if it is a


The Categories of a Hot Work Environment are

90 - 104 F = "Lower Order"

105 - 130 F = "Higher Order"

In assessing the heat stress potential of the workforce, begin by evaluating each individual by job description or specific duty. Make this evaluation daily, if necessary.

In addition to recognizing the differences of each worker's job category, each individual must be considered with respect to their physical conditioning and environmental exposure.


Calculate the aggregate heat index.

To derive the Aggregate Heat Index of any given task, subtract the base metabolic burn rate (1.0 calories per minute) from the caloric burn rate of the task being performed, and then add the result to the measured heat index, plus the heat load factors of the clothing worn by the subject worker, and the Effective Heat Index is derived. If the work is performed in full sunlight, multiply the result by 1.05 to compensate for solar load. An example follows.

85 F Actual Temperature

70 % Relative Humidity

93 F Calculated Heat Index
(See Attachment A)

Caloric Burn Rate of Task
3.5 Whole Body - Light

Heat Load Imposed by Clothing
0.09 T-Shirt
0.05 Briefs
0.14 Shirt - Light Short
0.32 Trousers - Heavy
0.04 Socks - Ankle
+ 0.08 Shoes - Boots

0.72 = Clothing Total

93 Calculated Heat Index
3.5 Caloric Burn Rate of Task
+ 0.72 Heat Load Imposed of Clothing

97.22 Total
- 1.0 Base Metabolic Rate

96.22 Aggregate Heat Index

x 1.05 Adjusting for Solar Load


Under the conditions provided in the example, the system of the worker performing the defined task in an environment with a heat index of 93 F responds as if the actual heat index were 96.22 F (101.03 F in full sunlight.) Performing this calculation is a prerequisite to planning work-rest cycles.

Plan a work-rest cycle. The crucial factor in preventing heat stress injury lies in keeping the core body temperature from exceeding 100.4 F. Under certain conditions, an individual may be able to maintain a core body temperature below this threshold, even though the calculated heat index is somewhat above this level. Such an individual would be one who is well acclimated to hot environments, in good health, with a system that is not overtaxed by activity. Other criterion would include ambient conditions that would permit (or enhance) the evaporation of sweat, thereby enabling (or enhancing) the operation of the body's blood cooling mechanism. Finally, in order to sustain the given activity, the individual would need a certain amount of water and sustenance to replace that which is lost through the perspiration and metabolic processes, and the individual would need periods of rest. If any component is absent, the individual will eventually experience heat stress. If any component is absent for an extended period of time, the individual will suffer heat stroke.

Sources to date seem very reluctant to provide definitive guidance on establishing work-to-rest cycles. The most explicit source examined during the research for this text was published by the American Conference of Governmental Industrial Hygienists (ACGIH) in their 1995-1996 Threshold Limit Values (TLVs) for Chemical Substances and Physical Agents and Biological Exposure Indices (BEIs). The rarity of substantial guidance on work cycle planning, and notice given to the widely drawn margins for error in that which is available, speak not only to the complexity of the human machine, but seem to beg for additional research on the topic of human activity in hot environments. Until such a time as adequate research is funded, employers will find themselves subject to what now represents the "best available technology." Consequently, the "due diligence" and "reasonable man" tenets, by which tort law determines the liability of employers with respect to worker injury, will hinge on these same vagaries.

The support text published in the TLVs on heat stress is qualified as being applicable only for workers who are acclimatized to existing conditions, dressed in light-weight clothing, and have an "adequate" intake of water and salt. Additional factors that decrease the recommended values are included to compensate for the effects of direct sunlight (solar load) and other than light-weight clothing. The tabulated data taken from the Biological Exposure Indices, Table 1 (p 89) prescribe the following work-rest regimen, and are expressed in terms of the wet bulb globe temperature (WBGT). These temperature closely correlate to those expressed on the Heat Index Chart (ATTACHMENT A) but do not compensate for solar load, insulative factors for clothing, caloric burn rate modifications, or health factors.

Work Load
Work-Rest Regimen Light Moderate Heavy

Continuous Work 86 F 80 F 77 F

75% Work-25% Rest 87 F 82 F 78 F

50% Work-50% Rest 89 F 85 F 82 F

25% Work-75% Rest 90 F 88 F 86 F

An interesting result is obtained when the recommended work-to-rest regimen in juxtaposition with specific heat indices is graphed. Although the various plotted points do not appear to indicate a strictly linear relationship between the three classifications of work, a generalized extrapolation to the 0% work to 100% rest point indicates that work should not be permitted when the heat index is at or above 91.4 degrees F (assuming all previous qualifications are met.) Yet, in Florida, if these guidelines were followed to the letter, it is highly unlikely that much outdoor work could be accomplished during the summer months.

To illustrate this point, temperature and humidity data furnished by the Meteorological Department at Florida State University was examined. The data from five key geographical points in Florida indicate that heat indices above 91.4 F may be expected from early May through late September, and the duration of heat indices above the extrapolated threshold may be expected from one to seven hours per day. Certainly, this marker is not intended to be used to determine when work should be halted; it is intended to serve only as the point where our concern should be heightened and the point where measures should be initiated to prevent heat stress injury. The work-rest cycle, only one component in the Heat Stress Prevention Plan, may be expected to vary on a day-to-day basis. It is ultimately determined by evaluating the data accumulated by using all the techniques described in this text. In summary: anticipate, know, teach, and be prepared.

ANTICIPATE the needs of employees. Furnish the materials that will be needed to prevent heat stress: water, shade, rest, and other administrative and engineering controls.

KNOW the health and physical capabilities of the employees (including both long- and short term variations in their general health and physical condition). Know the demands of the task in which they are engaged (the caloric burn rate). Know the effects of extenuating circumstances (e.g. heat load imposed by personal protective equipment, or "PPE"). Know the environmental conditions to which they are being exposed. Be prepared to make changes based on the health and safety needs of the workers. Teach employees the potential dangers of working in hot environments.

TEACH the warning signs of heat stress to all employees. Review these items periodically, and solicit feedback from each employee on an individual basis to ensure the learning process has had the desired effect.

BE PREPARED for all contingencies by constructing the worst case scenario and then developing a strategy to defeat it. Use the "if - then" principle.

There is an imminent challenge to the safety and health professionals in the State of Florida and that is to increase the collective awareness of the potential health threats imposed by working in hot environments. There is, likewise, a challenge to the employer which is perhaps best described as a commitment to support the research necessary to gain better understanding of occupational heat stress. From the standpoint of doing business, it is a prudent act on the part of the employer to support this research because it enables the employer to decrease workers' compensation expenditures and thereby maximize the profit margin. From a humanitarian view point, it is the right thing to do.