Hydrogen Sulphide (H2S)

 Hydrogen Sulphide (H2S)

Hydrogen Sulphide is a colorless, 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 craft 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” odor 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.