Lecture 17 - Heat Stress 11-10

Lecture 17 - Heat Stress 11-10 - Thermal
Environments 
...

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Unformatted text preview: Thermal
Environments 
 
 3
Types
 
Hot 
 
Neutral 
 
 
Cold
 Methods
for
Assessing
Thermal
Environments
 
Objec<ves
 
 
Physiological
responses
 
 
 
Sweat
rate,
body
&
skin
T°,
heart
rate
 
 
Performance
 
 
 
Motor,
cogniAve
 
Subjec<ves
 
 
Psychological
Comfort
 
 
 
Thermal
sensaAon
 
 
 
Acceptability
 Methods
for
Assessing
Thermal
Environments
(cont.)
 Mathema<cal
Models
 
Heat
exchange
 
 
see
formula 
Dynamic
model
of
human
thermal
regula<on 
 
 
 
 
 
 
Homeostasis
principle 
 
body
T°
=
Const. 
Hot
⇒

 
vasodilataAon
⇑
blood
flow,
⇑
HR
 
 
 
Then
⇑
sweat
rate
(evaporaAon) 
Cold
⇒

 
vasoconstricAon
⇓blood
flow,
⇓
HR 
 
 
Disadvantage:
feel
cold,
loss
of
tacAlity 
 
 
Then
⇑
shivering
(metabolic
heat)
 
 
Empirical
models 
 
 
"fit
data"
 Methods
for
Assessing
Thermal
Environments
(cont.) Relevant
Measures

 
Variables
affecAng
heat
exchange
 
Air
velocity,
Air
T°,
Radiant
T°,
humidity,
 
 
Clothing
insulaAon,
AcAvity
 Heat
Balance •
Heat
input
=
Heat
output
 
M


±


C


±


R


±


H


‐


E


=


S

 
If
S
≠
0
then
body
T°
⇑
or
⇓ •
Evapora<on
required 
E
req
=
(M
‐
W)
+
C
+
R
 •
Skin
wePedness

 

 
 
E
transformed
into
work
 Thermal
Environments:
Performance Generally
affected
in
extreme
environments
 and
long
exposure
 Motor
 
Manual
dexterity
(cold
or
T
>>
25°)
⇓
in 
physical
performance
could
be
due
to 


 
hypohydrataAon
or
dehydrataAon Cogni<ve,
Behavioral 
vigilance,
mental
tasks
 
(arithmeAc,
memory,
decision
speed) Decrements
difficult
to
predict 
 
 Thermal
Environments:
Performance Heat
represents
an
extra
load
on
the 
cardiovascular
system 
Blood
func<on:
 
 
O2
transport
 
 
+
used
as
cooling
fluid
to
dissipate
body
heat
 
 
CirculaAon
accelerated
(Heart
Rate
⇑) 
 
 
thus
circulaAon
Ame
⇓

and
O2
exchange
⇓ However
when
no
performance 
 decrement
is
observed
there
is
s<ll
 
 a
Physiological
cost
 Thermal
Environments
(cont.)
 Pathologies
 
Death
 
Damage
to
brain
funcAons 
Damage
to
limb
extremiAes 
White
finger
syndrome
(Raynaud's
syndrome) 
 
 
potenAaAon
with
vibraAon
exposure Acclima<za<on
 
⇑ 
in
sweat
producAon 
⇓
 
skin
T° 
⇓
 
Heart
rate
 ...
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This note was uploaded on 03/17/2010 for the course IOE 265 taught by Professor Garyherrin during the Fall '09 term at University of Michigan-Dearborn.

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