Hydrogen
Sulphide (H2S) Awareness
Hydrogen Sulphide (H2S)
Hydrogen
sulphide is a colourless, flammable, extremely hazardous gas with a “rotten
egg” smell. Some common names for the gas include sewer gas, stink damp, swamp
gas and manure gas. It occurs naturally in crude petroleum, natural gas, and
hot springs. In addition, hydrogen sulphide is produced by bacterial breakdown
of organic materials and human and animal wastes (e.g., sewage). Industrial
activities that can produce the gas include petroleum/natural gas drilling and
refining, wastewater treatment, coke ovens, tanneries, and kraft paper mills.
Hydrogen sulphide can also exist as a liquid compressed gas
Hazardous properties of
H2S gas
Hydrogen sulphide is heavier than air and may
travel along the ground. It collects in low-lying and enclosed,
poorly-ventilated areas such as basements, manholes, sewer lines, underground
telephone vaults and manure pits.
For work within confined spaces, use
appropriate procedures for identifying hazards, monitoring and entering
confined spaces.
The
primary route of exposure is inhalation and the gas is rapidly absorbed by the
lungs. Absorption through the skin is minimal. People can smell the “rotten
egg” odour of hydrogen sulphide at low concentrations in air. However, with
continuous low-level exposure, or at high concentrations, a person loses
his/her ability to smell the gas even though it is still present (olfactory
fatigue). This can happen very rapidly and at high concentrations, the ability
to smell the gas can be lost instantaneously. Therefore, DO NOT relies on your sense of smell to indicate the continuing
presence of hydrogen sulphide or to warn of hazardous concentrations.
In addition, hydrogen sulphide is a highly
flammable gas and gas/air mixtures can be explosive. It may travel to sources
of ignition and flash back. If ignited, the gas burns to produce toxic vapours
and gases, such as sulphur dioxide.
Contact
with liquid hydrogen sulphide causes frostbite. If clothing becomes wet with
the liquid, avoid ignition sources, remove the clothing and isolate it in a
safe area to allow the liquid to evaporate.
Health effects of H2S
exposure
Hydrogen
sulphide is both an irritant and a chemical asphyxiates with effects on both
oxygen utilization and the central nervous system. Its health effects can vary
depending on the level and duration of exposure. Repeated exposure can result
in health effects occurring at levels that were previously tolerated without
any effect.
Low
concentrations irritate the eyes, nose, throat and respiratory system (e.g.,
burning/ tearing of eyes, cough, shortness of breath). Asthmatics may
experience breathing difficulties. The effects can be delayed for several
hours, or sometimes several days, when working in low-level concentrations.
Repeated or prolonged exposures may cause eye inflammation, headache, fatigue,
irritability, insomnia, digestive disturbances and weight loss.
Moderate
concentrations can cause more severe eye and respiratory irritation (including
coughing, difficulty breathing, and accumulation of fluid in the lungs), headache,
dizziness, nausea, vomiting, staggering and excitability.
High
concentrations can cause shock, convulsions, inability to breathe, extremely
rapid unconsciousness, coma and death. Effects can occur within a few breaths,
and possibly a single breath.
Protection against H2S
exposure
Before
entering areas where hydrogen sulphide may be present:
1.
Air must be tested for the presence and concentration of hydrogen sulphide by a
qualified person using air monitoring equipment, such as hydrogen sulphide detector
tubes or a multi-gas meter that detects the gas. Testing should also determine
if fire/ explosion precautions are necessary.
2.
If the gas is present, the space/area must be ventilated continually to remove
the gas.
3.
If the gas cannot be removed, the person entering the space/area must use
appropriate respiratory protection and any other necessary personal protective
equipment, rescue and communication equipment. OSHA’s Confined Spaces standard
contains specific requirements for identifying, monitoring and entering
confined spaces.
Entering dangerous H2S
atmospheres
A
level of H2S gas at or above 100 ppm is Immediately Dangerous to Life and
Health (IDLH). Entry into IDLH atmospheres can only be made using: 1) a full face
piece pressure demand self-contained breathing apparatus (SCBA) with a minimum
service life of thirty minutes, or 2) a combination full face piece pressure
demand supplied-air respirator with an auxiliary self-contained air supply.
If H2S levels are below 100 ppm, an
air-purifying respirator may be used, assuming the filter cartridge/canister is
appropriate for hydrogen sulphide. A full face piece respirator will prevent
eye irritation.
If
air concentrations are elevated, eye irritation may become a serious issue. If
a half mask respirator is used, tight fitting goggles must also be used.
Workers
in areas containing hydrogen sulphide must be monitored for signs of
overexposure.
Definition of H2S Zones / Classified
Area Requirements
H2S-0 Zone / Areas
•
H2S present during normal
operations
• Cannot be made H2S free
• Warning Notices: skull-and-crossbones symbol; wording
advising; area classification; entry procedures
• Entry: Work Control Certificate-Permit
• Protection: positive pressure self-contained breathing
apparatus, or positive pressure airline breathing apparatus with independent escape
air supply
•
All staff involved in the work should be fully trained
H2S-1 Zone / Areas
• H2S may occur during normal operations
• Can be made safe for working
• Warning Notices: skull-and-crossbones symbol; wording
advising; area classification; entry procedures
• Entry: Work Control Certificate-Permit
• Before entry/during work: reduce the H2S concentration
to as low a level as possible by ventilation and other means
• Protection: portable and personal monitoring equipment
•
All staff involved in the work should be fully trained
H2S-2 Zone / Areas
• Normally free of H2S
• Possible contamination: system malfunction, leakage,
opening of an enclosed line or equipment
• Warning Notices: skull-and-crossbones symbol; wording
advising; area classification; entry procedures
• Alarm systems present
• Before entry: portable monitor (testing the atmosphere)
• Protection: portable and personal monitoring equipment
•
All staff involved in the work should be fully trained
H2S-2 Major Zone / Areas - additional
info/requirements
• Releases > 500 ppm
• Risk of serious irreversible health effects
• Entry control system (sign-in/sign-out)
H2S-2 Minor Zone / Areas - additional
info/requirements
• Releases < 500 ppm
•
Risk of minor reversible health effects
Before starting to work at an H2S site
You have to
• Have permission from the person responsible for the
site to enter the site
• Be familiar with the hazards of H2S
• Have had training in H2S
• Keep a tested H2S detector in the vicinity of the
breathing zone
• Have an escape mask / Respiratory Protection Equipment RPE if applicable
• Have determined the easiest escape route for oneself
In case of an H2S alarm
• Stop
all work
• Leave the area immediately
• Put on the escape mask
• Report the incident immediately
• Report to the person responsible for the area
• Follow further instructions
Do not attempt any rescue actions if you do not have
respiratory equipment or when you are alone.
NEVER attempt a rescue in an area that may contain
hydrogen sulphide without using appropriate respiratory protection and without
being trained to perform such a rescue.
Post by Indian Safety Association
www.doshti.com
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