Transcript Slide 1
DANGER
CONFINED SPACE
Special Training &
Precautions required
NO UNAUTHORIZED ENTRY
Risk Assessment of Oxygen Depletion and Hazardous Gas
Emissions at Mine Reclamation Sites
Ladan Mohammadi and John Meech
NORMAN B. KEEVIL INSTITUTE OF MINING ENGINEERING, UBC, Vancouver, B.C.
Confined Space Accident Features
Multiple deaths- rescuers are victims
Gases in Sulfide Waste Dumps
Making Confined
Spaces Safe
Oxidized region
Emission of air with low O2, or toxic gases
Dangerous emissions from surfaces and structures
Gas entry through soil
Sulfide oxidation and acid neutralization
First element: Potential danger
because of configuration
Intermittent danger from climatic variations
Potential flooding with water, soil, snow or grain…
Immediate threat to life or interference with escape
Schematic Representation of Fuzzy Risk Assessment
Rainfall
Rainfall
Rainfall
Oxygen
Oxygen
Final element: Danger guaranteed
because of gas emission
Oxygen
O2 consumed and CO2 produced
2002- An owner and a rescuer died in a winery
2003- A welder died in a barge hull.
X gt %O2 in the air at time t
2003- 4 workers died in a barge (2 others injured)
Ct Dissolved O2 in waterin the sump at time t (mg / L)
Ct * O2 equilibriu m concentration in sump water at time t (mg / L)
May 2006 - an environmental consultant,
- a project manager
- 2 paramedic
Sampling sump measured 2% O2 and 7% CO2
after Ritchie, 1994
Equilibrium dissolved-O2 in the water at 10oC
=12 mg/L)
If O2- depleted water (1 ppm O2 in water)
enters an enclosed space, oxygen can
be removed from air in the space
Depending on flow and volume, this can
become dangerous in hours or days
Static air in the sump (21% O2) in less
than 40 hrs, O2 in the sump drops to 17%
by O2- depleted water (1 ppm O2 in water)
BCMEMR advised Sampling Sheds to be
considered as confined spaces
Negative Energy- Air comes out of the pipe
Positive Energy- Air goes into the pipe
Energy has a cubic relationship with T
May 13-17, T rose to 20°C, P dropped
courtesy of
workSafeBC
YOUR LIFE IS
IN DANGER
This card could
save your life
O2-depleted effluent and air isolated from atmosphere
1- is situation an enclosed-space (3 sides)
(e.g. sump, depression, ditch,…)?
Yes
No
2- Are there O2- depleted water/air (toxic
gases) flowing into the space?
Yes
No
3- Is there a possibility of atmospheric
effects on the situation?
Yes
No
"Atmospheric risk" classification - linguistic terms
Fuzzy boundaries from high to low risk
O2 is compared to the normal level
Calculate the degree to which the space is safe
Atmospheric
Pressure and
Temperature
Gas
Temperature
Pathway
Properties
Distance
Gas releases
(pathways emission)
Fuzzy Rule-base
Gas
Concentration
Gas
Confinement
Dispersion
coefficient
(vertical)
Dispersion
coefficient
(horizontal)
Time
100
Gas
dispersed
Workers
exposed
Risk of an
Atmospheric
Hazard
Confined Space Hazard Variation
Hazardous - Fatality
10
Safe
Marg. Hazardous – Illness, need rapid treatment
Problem
Hazardous
1
Problem - Dizziness and side effects
Marg. Problem
Not
a
Marg. Prob. - No sign of feeling sick
0.1 Problem
Marg. Hazardous
Marg. Safe - No instant side effect
Marg. Safe
0.01
Safe – No adverse effect of gases
0 10 20 30 40 50 60 70 80 90 100
Not a Problem - No gas present
Confined Space Hazard Index
Conclusions
Recognizing a confined space hazard – MOST IMPORTANT ASPECT
Fuzzy risk analysis can apply to other types of contamination
References
A.I.M. Ritchie, 1994. Sulfide oxidation mechanisms: controls and rates of oxygen transport. Short Course Handbook on
Environmental Geochemistry of Sulfide Mine-Wastes, Mineral. Assoc. of Canada, 22 (ed. J. Jambor and D. Blowes), 201-245.
J. Bayah, J.A. Meech, G. Stewart, 1984. Oxygen Depletion of Static Air by Backfill Material at the Thompson Mine, Mining
Science & Technology, 1(2), 93-106.
Acknowledgement
Air in the shed directly connected to "bad" air in dump
Atmospheric conditions play a major role
Failure to identify the space and worker
entry into the space
Current reclamation regulations require acknowledgement of atmospheric problems
2005 - 1m of glacial till placed over dump and ditch
Shed was safe before change in drainage design
Step 5.
Exposure of workers
Atmospheric
Temperature
Atmospheric
Pressure
" inhales " <<<< 10°C <<<< "exhales “
Conversion of a ditch to drain may be problematic
2004 - ditch was covered as toe extended
Surface disturbances (erosion channel or
pits) or structures built on surface
Fuzzy Sets of Oxygen Level
Waste
Properties
Cover
Properties
Energy Into and Out of the Dump and Temperature
Rarely a problem if effluent is open to the air
Reclamation Activities at Sullivan
Mine - contribution to the Accident
Concentration
Fuzzy output values
Sampling sheds ( sampling / flow measurement)
Diversion ditches, drains and geo-membranes
Step 4.
Snow
P= 102 kPa
T = 20oC= 293 K
Water Flow Rate = 2000 l/hr = 33.33 l/min
Water volume in sump = 1200 l
Air Volume in sump = 4800 l
Sump Area = 2* 1.2 m2
Sump depth = 2.5 m
Operating Practices at Mine
Reclamation Sites
Covering and planting
Emission
Rain
Shed was in use for 5 years without problem
courtesy of
workSafeBC
Atmospheric conditions and pathway
properties
Step 3.
O2-depletion by water and dump gases
In 13 hrs, O2 in the sump drops to 17%
Accident identified as "unprecedented"
Waste properties, pH, climate, dump size
and age, cover properties.
Death
2001- A welder and 3 rescuers died in a barge.
Sullivan Mine Tragedy
Step 2.
O2 - depleted air
Generation
Sulfides, Surface Area, Air, Water
Groundwater flow
O2-depletion by water alone
1997- 2 workers overcame in a pulp mill.
The mining industry in B.C accounted for only 0.6 %
of the total B.C workforce from 1996 - 1999, yet it was
responsible for about 3.77 % of fatal work accidents
(27 fatalities in mining from a total of 715 in all sectors).
Reactivity
Oxygen
Chemical reactions
Controlled by dissolved- O2 in water, air diffusion,
cover permeability, internal temperature gradient,
climatic conditions, mineral quantity and reactivity,
and dump characteristics
Confined Space Fatalities by
O2- deficiency in B.C
2008, Sep- 3 workers died in mushroom facility
(and 3 other seriously injured)
Oxidation and chemical reactions
Step 1.
Degree of Belief
Photo From www.worksafebc.com
On-going atmospheric risk assessment of a mine reclamation site has typically been targeted at protecting the environment. Following a tragic accident that occurred at the Sullivan
mine in Kimberley, B.C., in which 4 people died of asphyxiation in a sampling shed, it is now clear that an occupational health and safety problem exists with the emission of
O2- depleted gases from within a mine waste dump. This poster describes an attempt to create a Risk Assessment method based on Artificial Intelligence methods to characterize
the potential for dangerous confined space situation at a mine reclamation site before such an accident may occur again.
The Sullivan Accident Technical Advisory Panel: Walter Kuit and Bruce Dawson from Teck Cominco;
POCKET SAFETY CARD
Don’t Enter
Enter
Ricci Berdusco, Phil Pascuzzi, and Al Hoffman from B.C. MEMPR; Clem Pelletier from Rescan Environmental;
Andy Robertson from Robertson GeoConsultants; Ward Wilson and John Meech from UBC;
Mike O'Kane and Mark Phillip from O'Kane Consultants; and Daryl Hockley from SRK.