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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.
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, 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.
(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.
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, 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, 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, the sixth level of heat stress, is a KNOWN KILLER, and ALWAYS constitutes a medical emergency of the highest magnitude.
EMERGENCY MEDICAL ATTENTION IS CRUCIAL
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.
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.
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
HOT WORK ENVIRONMENT
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.
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
101.03 TOTAL HEAT 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
(Hourly)
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.