An overview of Canadian heat stress research related to mining - SME

An overview of Canadian heat stress
research related to mining
Stephen Hardcastle, G. Kenny, & C. Allen
14 th U.S./North American Mine Ventilation
Symposium, Salt Lake City, Utah, June 17-20, 2012

Controlling personnel heat exposure
in Canada’s deep and highly
mechanized mines
• Project developed in 2004
• Base/precious metal industry identified heat
stress/management as a major challenge
affecting productivity and operating costs
• Project started in 2005
• Current research nearing completion
• Guidelines, workbook, further data analysis and
“Communicating the Science” will continue into
2013
2

Physical and mechanical characteristics
of selected mechanized mining tasks
• In situ characterization – motion,
loads, duration frequency, video
analysis etc. of 36 subjects
across six typical occupations:
drilling, ore transport, bolting,
shotcrete, support services
• In situ measurement of energy
cost (O 2 ), skin & core
temperatures for the typical
occupations
3

General Services
16% 25%
14%
18%
27%
Longhole Drilling
3%
6%
21%
23%
47%
Shotcrete
6%
4%
5%
43%
42%
Bolting
10%
11%
19%
29% 31%
Ore Transport
5%
5%
22%
30%
38%
Rest (0-114 W)
Light (115-234 W)
Moderate ( 235-359 W)
Heavy (360-469 W)
Very Heavy (470+ W)
Work intensity (Qualitative)
• Non-thermally stressful
environment
• 6-7 hrs video per subject
• ISO 7243 classification
• All groups include some “Very
Heavy” work
• Overall average “Light” to
“Moderate”
• Average work to rest ratios ≈2:1
through ≈7:1, maximum ≈72:1
• Used to define standard exercise
4

Energy & temperature (Quantitative)
• Non-thermally stressful environment
• 5-6 hrs physiological monitoring per subject
• Generally confirmed video assessment
• LHD operator upgraded to Moderate task
• General Services and Bolting have highest
demands at 290-330 W with peaks of 530 W
• Provided foundation for controlled laboratory
tests at ≈360-400 W
• Temperature pill showed core temperatures
>38 C in all work categories, at varying times
for up to 60 minutes in middle aged miners
5

Extreme task – Mine Rescue
• Cool environment (17 C/15 C dry/wet)
• Simulated ramp rescue – three climbs,
up to 150 kg load, 8 grade, for 250 m
plus light activities and descents
• Confirmed mine rescue as “Very
Heavy” task for prolonged duration
>470 W for > 60 minutes
• Breathing apparatus, static carry and
Nomex clothing adds to the severity of
the task
• Core temperatures reached >39 C
6

Laboratory controlled environment
studies
• Replication of typical mining tasks
• Simulation of moderate to extreme
environments
• Influence of clothing †
• Intermittent work & recovery
practices †
• Combined effects of clothing,
• work and humidity †
• Acclimation
† Study added based upon findings
7

Rectal Temperature (ºC)
38.5
38.0
37.5
37.0
36.5
Laboratory simulation
- Environmental chamber
Subjects unable to complete test
Core Limit
1 2 3 4 5 6
0 20 40 60 80 100 120
Time (min)
Environment
39ºC 60RH
35ºC 80RH
35ºC 60RH
35ºC 40RH
30ºC 60RH
Work
1: 386 W
2: 360 W
3: 345 W
4: 227 W
5: 365 W
6: 285 W
• 2- hr exercise
protocol
• “Standard” mine
gear
• WBGT’s 26 to
34 C
• Exposure more
related to WBGT
than t WB
8

Clothing study
- “Gold standard” calorimeter
Semi-nude
(Control)
Wicking
Undergarment
Coveralls
Full PPE
Work Pant
Wicking T-Shirt
• Clothing
• 2-3 W
resolution of
dry and
evaporative
heat loss,
and body
heat storage
Combined 2-layer arrangement
9

Esophageal Temperature (ºC)
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
Clothing study
- Potential to affect heat storage
Exercise
37.66ºC
37.25ºC
0 15 30 45 60 75 90 105 120
Time (min)
Control - Shorts
Undergarment only
Mine gear only
Mine gear + undergarment
Recovery
• Less heat loss with
coveralls - core
temperature rises
continually
• Sportswear similar
to being naked
• Coveralls store
more heat when
resting
• Pant with t-shirt
perform similar to
semi-nude control
10

Work: Recovery practices
- ACGIH Screening Criteria for TLV/Action Limit, ºC
Demand Category
(median)
Allocation
Light
180W
Moderate
300W
360 W
Heavy
415W
Very Heavy
520W
Work/Recovery TLV AL TLV AL TLV AL TLV AL
75% - 100% Work 31.0 28.0 28.0 25.0
50% -75% Work 31.0 28.5 29.0 26.0 27.5 24.0
25% - 50% Work: 32.0 29.5 30.0 27.0 29.0 25.5 28.0 24.5
0% - 25% Work 32.5 30.0 31.5 29.0 30.5 28.0 30.0 27.0
• Increased environmental conditions offset by greater recovery
11

Rectal Temperature (°C)
Work: Recovery practices
- Young subjects
38.2
38.0
37.8
37.6
37.4
37.2
37.0
0
100% Continuous, 28.0 t wbgt
75:25% (6 x 15:5 min), 29.0 t wbgt
50:50% (4 x 15:15 min), 31.0 t wbgt
25:75% (2 x 15:45 min), 31.5 t wbgt
15 30 45 60 75 90 105 120
Time (min)
• Final core
temperature
decreases
through trials
• Recovery period
more than
compensates for
the higher
environmental
temperature
• “Active” recovery maintaining blood circulation is preferable
12

Rectal Temperature (°C)
Combined effects
- Clothing, work practice & environment
38.2
38.0
37.8
37.6
37.4
37.2
37.0
0
Hot/dry: 46 t db , 22 t wb ; Warm/wet: 33 t db , 27 t wb
75:25% (6 x 15:5 min), 29.0 t wbgt
15 30 45 60 75 90 105 120
Time (min)
• Coveralls caused
highest core
temperature and
change in body heat
content
• Single parameters,
such as T re , taken
alone may
misrepresent the
human/clothing
system interaction
with environment
13

Acclimation
- Adaptation and retention of thermoregulatory changes
• 2 age groups of 8 persons (20-25 yrs & 50-65 yrs)
• 28 day semi-nude assessment, 14/14 days
acquisition and loss performed in a 35 C/20%RH
environment
• Same incremental intermittent exercise protocol
followed on all 14 days of heat training
• Adaptation tested on five occasions – Day 1, 7,
14, 21 & 28
• Other functions such as sweat production
assessed on non-calorimeter days
14

Acclimation
- Adaption phase heat production & loss
Heat Production & Total Heat Loss (W)
800
700
600
500
400
300
200
100
Baseline 300 W/m 2 350 W/m 2
400 W/m 2
WORK
M-W
Day 0
Day 7
Day 14
HEAT
LOSS
GREATER
HEAT
LOSS
• 20-25 yr subjects
without any prior
acclimation
• Days 0-14 show
progressive
decrease in heat
retained
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Time (min.)
15

Heat Production & Total Heat Loss (W)
Deacclimation
- Heat production & loss
800
700
600
500
400
300
200
100
Baseline 300 W/m 2 350 W/m 2
400 W/m 2
WORK
M-W
Day 14
Day 21
Day 28
HEAT
LOSS
REDUCED
HEAT
LOSS
• Days 14-28 show
progressive loss of
any adaptation
• Similar effects
seen for
evaporative heat
loss and core
temperature
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Time (min.)
16

Change in body heat content (kJ)
Acclimation
- Cumulated heat storage
Induction phase Decay phase • End of 3 rd exercise
• Young subjects
showed significant
adaptation over 14
days to exercising in
the heat
• However, the effects
of this first heat
training appears to
be short lived
Day 0 Day 7 Day 14 Day 21 Day 28
17

Parallel heat stress related studies for
at risk populations and support
• Budget within DMRC was limited
• Other funding sources levered to fill gaps and
extend scope
• Workplace Safety Insurance Board (WSIB) of
Ontario
• Natural Science and Engineering Research
Council (NSERC), Canada
• Canadian Foundation for Innovation
• Precarn Inc. (Pre commercialization iICT funding agency)
• University of Ottawa Research Chair
18

Age, sex & health
Personal factors can affect how
individuals respond to the heat and their
ability to cool
• The mining workforce in Canada is aging
• Agnico (~ 40 yrs), Mine Rescue (25-62 yrs)
• Older subjects may not be as fit or healthy,
type-2 diabetes (T2DM) is becoming more
common
• Muscle and sweating capacity can diminish
with age
• Females typically smaller than males
19

Age, sex & health
Generalized results:
• Young vs Middle-aged - subjects matched
for fitness typically exhibit similar responses
and capacities for moderate work in
temperate conditions
• Males vs Females - females disadvantaged
by smaller body mass, greater BMI for a
given workload
• Young vs Middle-aged vs Old – study ongoing
• Healthy vs T2DM – added comparison
20

Air velocity, sweating & skin blood flow
- Core heat needs to reach the skin surface
• Under current mining Canadian mining
conditions the evaporation of sweat has great
cooling potential
• Skin blood flow and sweating are affected by age
• Evaporation at the skin surface is affected by air
velocity
• A study comparing air velocities of 0.5, 1.5 & 3.0
m/s for both young and older subjects is ongoing
21

Biomarkers & cognitive function
Heat reactions and impairment
• Exercise and/or working in the heat can stimulate a
stress response within the body
• A study of cortisol, a steroid hormone released under
stress, and interluken-6, a protein secreted to stimulate
the immune system, compared their production under
hot/dry and warm/wet conditions
• Heat not only affects physical ability but also
compromise mental capacity and thereby vigilance
• Another study is evaluating the effects of sleep debt and
shift work on fatigue prior to considering heat exposure
22

Personnel cooling & monitoring
Specific solutions & informed management
•Unsuccessful development of garment from novel
laboratory bench proven hydrophobic membrane
with controlled evaporation properties
• Phase change “Ice Vest” – Calorimeter based studies proved
technology as a special situation countermeasure as it could
extend work duration in the heat
•Considering all the qualifiers and modifiers a
single parameter monitor may be inadequate
• A smart ambulatory monitor including ECG, respiration,
movement, skin impedance and temperature was
prototype tested & will be part of the cognitive study
23

Non-physiological studies …..
• In addition to studying the mechanics of heat
stress it was also important for the industry to
understand:
• How to accurately measure the environment
• The cause of that environment
• How to provide cooling
The final objective of the DMRC funded research
is to produce a “design” manual detailing all the
research and studies to allow mines to develop
more informed heat management strategies.
24

Evaluating & understanding the environment
- Sources of heat and their measurement
•The research included an in-depth
evaluation of heat stress meters
• Study showed t DB and %RH are the most
reliably measured parameters
• Study showed most “hybrid” meters are
untraceable or are inadequate for deep mines
•An assessment of heat sources showed
autocompression was the primary cause
of hot conditions in Canada’s deep mines
• Autocompression superimposed on surface
climate dictate the thermal quality of air
Heat Added in Summer (No Fans, No Cooling)
271 kW
2% Net Heat Gain 13,693
Autocompression
98%
13,422 kW
25

Moderating the environment
- Cooling strategies
•The DMRC contracted BBE to
produce a “A design manual
for Canadian mine cooling
plants”
• Recognizes sub-zero surface winter
conditions, short summers, low rock
thermal properties
• Considers surface and underground
mechanical installations
• Produced a series of decision trees
• Subject of a short-course at this
symposium
26

Moderating the environment
- Natural cooling
•Expand the concept of using “cold
stopes”
•Testing of Vale’s prototype Modular
Thermal Transfer Unit (MTTU)
•Recycled sea-containers with water
sprays
•Efficient & cheap heat transfer
during winter when ice forms
•Summer cooling capacity needs
further development but is
promising small alternative
27

Summary
• When completed next year, the DMRC will have spent
$3.5M, almost 50% of its cash funding on “heat stress”
related research
• The mines and others have also made significant inkind
contributions, i.e. freeing up manpower for the mine
based studies
• The DMRC work has also resulted in the University of
Ottawa and others in being able to lever another $2M+
of funding for parallel and supporting research activities
28

Conclusions
• Understanding the reaction of human/clothing systems
with the environment is complex
• The physiological studies supported by direct
calorimetry are bringing a new knowledge to heat
exposure management
• The initial goal of developing a “new” criteria has been
replaced by gaining a greater comprehension of the
factors that limit existing criteria
• Combined the physiological and non-physiological
research is allowing Canadian mines to develop more
specific work practices and solutions as applicable to
their individual requirements
29

Acknowledgements
• The miners & staff at Agnico Eagle’s Laronde mine
• The Ontario Mine Rescue and mine volunteers
• The laboratory test subjects young & old
• The University of Ottawa research personnel
• The Deep Mining Research Consortium – without their
insight, patience & funding this research may not have
taken place
Questions ???
30