Title: 
Headings:  HEAT STRESS AND HEAT STRAIN
HEAT
 
STRESS
 
AND
 
HEAT
 
STRAIN
 

.'tfd-®A11
 


Content: He~at
 
Stress
 
is
 
the
 
net
 
heat
 
load
 
to
 
which
 
a
 
worker
 
may
 
be
 
exposed
 
from
 
the
 
combined
 
contributions
 
of
 
metabolic
 
heat,
 
environmental
 
factors,
 
(i.e.,
 
air
 
temperature,
 
humidity,
 
air
 
movement,
 
and
 
radiant
 
heat),
 
and
 
clothing
 
require
ments. A
 
mild
 
or
 
moderate
 
heat
 
stress
 
may
 
cause
 
discomfort
 
and
 
may
 
ad
versely
 
affect
 
performance
 
and
 
safety,
 
but
 
it
 
is
 
not
 
harmful
 
to
 
health. As
 
the
 
heat
 
stress
 
approaches
 
human
 
tolerance
 
limits,
 
the
 
risk
 
of
 
heat-related
 
disor
ders
 
increases. Heat
 
Strain
 
is
 
the
 
overall
 
physiological
 
response
 
resulting
 
from
 
heat
 
stress. The
 
physiological
 
responses
 
are
 
dedicated
 
to
 
dissipating
 
excess
 
heat
 
from
 
the
 
body. Acclimatization
 
is
 
a
 
gradual
 
physiological
 
adaptation
 
that
 
improves
 
an
 
indi
vidual's
 
ability
 
to
 
tolerate
 
heat
 
stress. Acclimatization
 
requires
 
physical
 
activity
 
under
 
heat-stress
 
conditions
 
similar
 
to
 
those
 
anticipated
 
for
 
the
 
work. With
 
a
 
recent
 
history
 
of
 
heat-stress
 
exposures
 
of
 
at
 
least
 
two
 
continuous
 
hours
 
(e.g.,
 
5
 
of
 
the
 
last
 
7
 
days
 
to
 
1
0
 
 
of
 
14
 
days),
 
a
 
worker
 
can
 
be
 
considered
 
acclimatized
 
for
 
the
 
purposes
 
of
 
the
 
TLV®. Its
 
loss
 
begins
 
when
 
the
 
activity
 
under
 
those
 
heat
 
stress
 
conditions
 
is
 
discontinued,
 
and
 
a
 
noticeable
 
loss
 
occurs
 
after
 
four
 
days
 
and
 
rT)ay
 
be
 
completely
 
lost
 
in
 
three
 
to
 
four
 
weeks. Because
 
acclimatiza
tion
 
is
 
to
 
the
 
level
 
of
 
the
 
heat
 
stress
 
exposure,
 
a
 
person
 
will
 
not
 
be
 
fully
 
accli
matized
 
to
 
a
 
sudden
 
higher
 
level;