Post on 23-Dec-2015
Risk Assessment of Oxygen Depletion and Hazardous Gas Risk Assessment of Oxygen Depletion and Hazardous Gas Emissions at Mine Reclamation SiteEmissions at Mine Reclamation Sitess
Ladan Mohammadi and John Meech Ladan Mohammadi and John Meech
NORMAN B. KEEVIL INSTITUTE OF MINING ENGINEERING, UBC, Vancouver, B.C.NORMAN B. KEEVIL INSTITUTE OF MINING ENGINEERING, UBC, Vancouver, B.C.
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Atmospheric conditions and pathway properties
Reactivity
Generation
Emission
Concentration
Exposure of workers
Death
Surface disturbances (erosion channel or pits) or structures built on surface
Waste properties, pH, climate, dump size and age, cover properties.
Sulfides, Surface Area, Air, Water
Failure to identify the space and worker entry into the space
O2 - depleted air
Schematic Representation of Fuzzy Risk Assessment
Time
Distance Pathway Properties
Gas Temperature
Atmospheric Pressure and Temperature
Gas Concentration
Fuzzy Rule-baseFuzzy Rule-baseGas
dispersedDispersion coefficient (horizontal)
Dispersion coefficient (vertical)
Gas releases (pathways emission)
GasConfinement
Workers exposed
Risk of an Atmospheric Hazard
Atmospheric TemperatureAtmospheric Pressure
Snow
Waste Properties
Cover Properties
Rain
Oxygen
Chemical reactions
Oxidation and chemical reactions
Oxygen
Oxygen Oxygen
Rainfall
Groundwater flow
Rainfall Rainfall
after Ritchie, 1994
Oxidized region
Making Confined
Spaces Safe
1997- 2 workers overcame in a pulp mill.
2001- A welder and 3 rescuers died in a barge.
2002- An owner and a rescuer died in a winery
2003- A welder died in a barge hull.
2003- 4 workers died in a barge (2 others injured)
2008, Sep- 3 workers died in mushroom facility (and 3 other seriously injured)
2004 - ditch was covered as toe extended
2005 - 1m of glacial till placed over dump and ditch
O2-depleted effluent and air isolated from atmosphere
Air in the shed directly connected to "bad" air in dump
Shed was safe before change in drainage design
Atmospheric conditions play a major role
Sulfide oxidation and acid neutralization
O2 consumed and CO2 produced
Controlled by dissolved- O2 in water, air diffusion, cover permeability, internal temperature gradient, climatic conditions, mineral quantity and reactivity, and dump characteristics
" inhales " <<<< 10°C <<<< "exhales “
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
Multiple deaths- rescuers are victims
Emission of air with low O2, or toxic gases
Dangerous emissions from surfaces and structures
Gas entry through soil
Intermittent danger from climatic variations
Potential flooding with water, soil, snow or grain…
Immediate threat to life or interference with escape
DANGERCONFINED SPACE
Special Training & Precautions required
NO UNAUTHORIZED ENTRY
Photo From www.worksafebc.com
May 2006 - an environmental consultant, - a project manager - 2 paramedic
Sampling sump measured 2% O2 and 7% CO2
Shed was in use for 5 years without problem
Accident identified as "unprecedented"
BCMEMR advised Sampling Sheds to be considered as confined spaces
Sullivan Mine Tragedy
Reclamation Activities at Sullivan Mine - contribution to the Accident
Confined Space Fatalities byO2- deficiency in B.C
Confined Space Accident Features
O2-depletion by water alone
Gases in Sulfide Waste Dumps
The Sullivan Accident Technical Advisory Panel: Walter Kuit and Bruce Dawson from Teck Cominco;
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.
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.
First element: Potential danger because of configuration
Final element: Danger guaranteed because of gas emission
Energy Into and Out of the Dump and Temperature
Conclusions Recognizing a confined space hazard – MOST IMPORTANT ASPECT
Current reclamation regulations require acknowledgement of atmospheric problems
Fuzzy risk analysis can apply to other types of contamination
References
courtesy of workSafeBC
courtesy of workSafeBC
Operating Practices at MineReclamation Sites
Sampling sheds ( sampling / flow measurement)
Rarely a problem if effluent is open to the air
Conversion of a ditch to drain may be problematic
Covering and planting
Diversion ditches, drains and geo-membranes
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
1- is situation an enclosed-space (3 sides) (e.g. sump, depression, ditch,…)?
2- Are there O2- depleted water/air (toxic gases) flowing into the space?
3- Is there a possibility of atmospheric effects on the situation?
Yes No YOUR LIFE IS
IN DANGER
This card couldsave your life
Yes No
Yes No
Don’t Enter EnterPOCKET SAFETY CARD
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)
"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
Fuzzy Sets of Oxygen Level
Hazardous - Fatality
Marg. Hazardous – Illness, need rapid treatment
Problem - Dizziness and side effects
Marg. Prob. - No sign of feeling sick
Marg. Safe - No instant side effect
Safe – No adverse effect of gases
Not a Problem - No gas present
Fuzzy output values Confined Space Hazard Variation
0.01
0.1
1
10
100
0 10 20 30 40 50 60 70 80 90 100Confined Space Hazard Index
Deg
ree
of
Bel
ief
Hazardous
Marg. Hazardous
Safe
Not a
Problem
Marg. Safe
Marg. Problem
Problem
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).
)/(*
)/(
%
2
2
2
LmgttimeatwatersumpinionconcentratmequilibriuOC
LmgttimeatsumptheinwaterinODissolvedC
ttimeatairtheinOX
t
t
gt
O2-depletion by water and dump gases
P= 102 kPaT = 20oC= 293 KWater Flow Rate = 2000 l/hr = 33.33 l/minWater volume in sump = 1200 lAir Volume in sump = 4800 lSump Area = 2* 1.2 m2
Sump depth = 2.5 m
In 13 hrs, O2 in the sump drops to 17%