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%