Transcript Termination of Response

ST-7.24
H2S Safety
P.A.W.S for thought
“No hazards down here mate!
How is Hydrogen Sulphide formed
H2S is a by-product formed when organic matter
decays
It is generated as a common by-product of
industrial and manufacturing processes
Hydrogen Sulphide is formed under low oxygen
conditions when sufficient amounts of Sulphur
and bacteria are present, e.g.
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Oil and gas reservoirs
Sewers and sewage processing facilities
Dark damp places where bacteria is present
Key Hazard Data
• Description
– Colourless gas: Offensive strong odour similar to rotten eggs.
• Fire and Explosion Hazard:
– Flammable gas, forms explosive mixtures with air.
• Flammable Range:
– LEL: 4.3% / UEL: 45%.
• PEL
– 20 PPM.
• IDLH
– 100 PPM
• Vapour Density:
– 1.2, (vapours are heavier than air)
• Chemical Abstract Service (CAS) Number
– 7783-06-4.
Concentration Levels & Effects
Concentration
Health Effects
10 ppm
Beginning eye irritation
50-100 ppm
Slight respiratory tract irritation after 1 hour exposure.
100 ppm
Coughing, eye irritation, loss of sense of smell after 2-15 minutes.
Altered respiration, pain in the eyes, and drowsiness after 15-30
minutes followed by throat irritation after 1 hour. Several hours
exposure results in gradual increase in severity of these
symptoms and death may occur within the next 48 hours
200-300 ppm
500-700 ppm
700-1,000 ppm
1,000-2,000ppm
Severe respiratory tract irritation after 1 hour of exposure.
Possible pulmonary edema (fluid in the lungs).
Loss of consciousness and possibly death in 30 minutes to 1
hour.
Rapid unconsciousness, loss of respiration, and death after 1-3
minutes.
Unconsciousness at once, loss of respiration and death in a few
minutes. Death may occur even if individual is removed to fresh
air at once.
Hazardous Characteristics
Toxic
H2S is the second most toxic gas
known to man.
The most toxic is Hydrogen Cyanide
PEL of H2S = 10 ppm
PEL of HCN = 10 ppm
H2S as an Asphyxiant
• Asphyxiants
– Interfere with body’s ability to use oxygen
• Chemical Asphyxiants interfere with
– Oxygen transportation via hemoglobin or
– Oxygen utilization by mitochondrial
– cytochrome oxidase (cyt a,a3)
Asphyxiants
Typical
Toxicants
Simple
Asphyxiant
Carbon dioxide
Propane
Butane
Chemical
Asphyxiant
Isobutyl nitrite
Carbon
monoxide
Hydrogen
cyanide
Hydrogen
Sulphide
Hydrogen azide
Predominant
Route of
Exposure
Predominant
Targets of
Toxicity
Predominant
Toxicodynamics
Inhalation
Cardiovascular
Disability
Displacement of oxygen
from ambient
atmosphere
Cardiovascular
Disability
Interfere with oxygen
transportation in blood
or oxygen utilization in
other tissues
Inhalation
Toxic Hazard, Question
• If the flare stack is burning away 100,000ppm
H2S and is burning at 80% efficiency, what is
the ppm of H2S in the exhaust plume?
100,000ppm. The flare stack is burning
80% of the volume not the concentration.
Hazardous Characteristics
When H2S is burned, it produces
Sulphur Dioxide “SO2”
–
Short-term exposures to high levels of
Sulphur Dioxide can be lifethreatening.
–
Exposure to 100 ppm of Sulphur
Dioxide is considered immediately
dangerous to life and health (IDLH)
–
PEL for SO2 is 2 ppm
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Sulphur Dioxide may cause heart
problems and respiratory disorders in
Hazardous Characteristics
Iron Sulphide
H2S reacts with iron and steel which forms iron
sulphide which can be Pyrophoric !
Hazardous Characteristics
Metallurgy
H2S may react with iron and steel causing
hydrogen embrittlement and/or sulfide stress
cracking. This lowers safety factors in tubular
and pressure vessels.
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Hazardous Characteristics
Corrosive
H2S dissolves in water to form a weak
acid that corrodes and pits metals.
How do we control this toxic gas?
• Engineering Controls
– Ventilation
• Natural
• Manufactured
– Flare Stack
– Venting
• PPE
– Supplied Air
Respirator
• SCBA
• Work line
• Escape Pack
Preventing Exposure
• Personnel who are working on sites or in locations
that may have H2S present should be provided with
appropriate PPE including a personal H2S monitor.
• Any site that has the potential for H2S shall be noted
and workers informed of the potential hazards.
• Look for signs or other indicators that demonstrate the
potential for H2S at the site.
• Ensure that you have a properly functioning H2S
monitor prior to entering a site with the potential for
H2S exposure.
• Supplied Air Respiratory (SAR) escape may be
required in some situation and this is to be addressed
in the Site Specific Plan and/or Risk Assessment
Atmospheric Monitoring
Atmospheric monitoring should be done
whenever there us potential for concentrations of
H2S to be released
This includes
– Confined space entry
– When potential for exposure exists
Monitoring needs to be undertaken for
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Toxicity
Flammability
Oxygen
Hydrogen Sulphide (H2S) Detection
Zero Maintenance
Sensor Range 0-100 ppm
Low Alarm 10 ppm
High Alarm 15 ppm
-40 to +50 C
Multigas detector
Colourmetric indicator tubes
There are 11 different H2S
detector tubes available for
H2S.
Recommended Tube is:
Drager Hydrogen Sulphide 2/b Tubes
Range: 1 - 60 ppm
Drager 8101961 Detector Tubes
PID and H2S
IE =10.45 EV
10.6 EV Bulb CF = 3.3
11.7 EV Bulb CF = 1.5
WARNING
NRC use 10.6 EV
on Isobutylene so
multiplied by 3.3
reading. PID will
Dioxide
Bulb units calibrated
any reading must be
to get the actual
not detect Sulphur
Escape Guidelines
Every facility or operations site that has the
potential for H2S Exposure should have an
emergency response plan
All personnel working in such a location should
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Know the alarm system
Know where the potential sources are located
Know the wind direction
Know where safe zones and muster points are
located
Know the evacuation routes
Know where emergency respirators are located
H2S First Aid
GENERAL FIRST AID CONSIDERATIONS
•
Fresh air ! (Rescuers must exercise caution!)
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If unconscious/not breathing – immediately provide
rescue breathing.
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Call a doctor ASAP!
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Give oxygen after cleaning oil from the injured
employee’s face.
Summary
Summary
• Acute Risk: Moderate to high – respiratory failure,
cardiac and neurological damage, ocular irritation
• Small range of significant effects – many will tolerate
50 ppm; some fatalities, many injuries at 500 ppm
• Odour not dependable to detect; use meters,
detectors
• Use air supplied respirators for rescue; Provide O2 /
CPR
• Explosive, may collect in low areas
• Exposure concentrations may change without
warning when low ventilation rates exist
Stay out – Stay alive
H2S
NEVER FORGET THAT HYDROGEN
SULPHIDE IS A DEADLY GAS.
TAKE NO CHANCES WITH IT!
KNOW WHAT CONCENTRATION OF THE
GAS IS PRESENT BEFORE DOING ANY
WORK IN IT.
H2S Warning signs
Its odour is NOT a reliable warning signal because
higher concentrations of the gas temporarily
destroys the sense of smell. This is the primary
reason for employees not detecting the presence of
H2S and consequently inhaling a lethal amount. The
only positive means is by testing with an approved
H2S detector.
DO NOT RELY SOLELY ON THE SENSE OF
SMELL!