During a maintenance shutdown at a natural gas processing facility in northeastern B.C., workers were exposed to mercury vapour when a number of vessels were opened. The site was shut down and workers were removed from the plant area. Mercury was identified in air samples collected from the vessels, and some of the exposed workers required treatment at a local hospital.

This document describes the health hazards posed by mercury and explains the presence of mercury in natural gas production and processing equipment. It also describes how to reduce the risk of exposure to mercury in natural gas facilities.

What is mercury?

Mercury is a heavy, dense metal that is liquid at room temperature. The freezing point of mercury is below minus 38 degrees Celsius. The liquid is so dense that a bowling ball would float in it.

Liquid mercury is quite volatile. When exposed to air, mercury metal vaporizes and can be inhaled. The warmer the temperature, the more quickly mercury vapour can get into the air.

Where is mercury used?

Mercury and its compounds have been used for a wide variety of purposes including:

A natural gas processing facility

Mercury in gas processing and production equipment

Mercury, in a number of chemical forms, is a natural component of oil and gas and may be present at high concentrations in some formations. Heat and pressure can liberate mercury from geological deposits. The mercury then migrates, as a vapour, to the oil and gas "traps."

When these gas reservoirs are produced and the processed fluids are cooled, liquid mercury can condense within heat exchangers, separators, coolers, valves, and piping.

Mercury can form amalgams with a variety of metals in processing equipment, resulting in corrosion. When this equipment is taken apart for maintenance or repair, workers can be exposed to mercury vapour. Work activities that may carry a risk of exposure in gas processing facilities include:

What are the health effects of mercury exposure?

Liquid mercury can affect human health through skin contact, by swallowing, and by breathing the vapour. Most worker exposure occurs through inhalation of mercury vapour.

Chronic (long-term) exposure to high concentrations of mercury vapour affects the central nervous system and can cause:

Gum disease can also be an early sign of chronic mercury exposure. The brain and kidneys are particularly susceptible to damage from mercury.

Contact with mercury can also cause irritation and burns to the skin and eyes.

Occupational exposure limits

Employers must ensure workers are not exposed to mercury levels above the occupational exposure limits (OELs). The OELs for mercury in B.C. are very low—an 8-hour time-weighted average (TWA) of 0.025 milligrams per cubic metre (mg/m3) for elemental mercury and inorganic compounds of mercury. Mercury—Methyl, as Hg has an OEL of 0.01 mg/m3.

Mercury is also an ALARA substance, meaning exposure must be kept as low as reasonably achievable, due to its potential for absorption through the skin and effects on the reproductive system.

Owner responsibilities

Owners must conduct a hazardous materials survey and a risk assessment for potentially hazardous contaminants (including mercury) at their facilities. This information must be kept on site and communicated to all contractors who will perform work at these locations.

Employer responsibilities

Employers must develop and implement an effective exposure control plan (ECP). An ECP explains the work procedures and other controls that will be used to reduce workers’ risk of exposure to mercury.

An ECP for a workplace where workers may be exposed to mercury must include:

Worker responsibilities

To help reduce the risk of exposure to mercury, workers (including subcontractors) must:

Sampling for mercury

Choosing the correct sampling method for mercury can be difficult because each has its own potential problems (e.g., interferences).

Sampling methods currently available include:

Monitoring for mercury vapour using direct-read instruments

Reducing the risk of exposure

The risk of worker exposure to mercury can be reduced by using the following controls:

Personal protective equipment

The following PPE can be used, along with engineering and other controls, to protect workers from exposure to mercury:

Workers who use respirators must be clean-shaven where the respirator seals with the face to ensure a good seal.

PPE should also include a chemical-resistant, fire-rated suit, goggles that seal to the face (if a full-face respirator is not worn), and gloves (preferably nitrile).

Workers wear respirators while testing for mercury

Personal hygiene

Workers should wash their hands before eating or smoking to minimize contact with mercury.

Employers should do the following:

First aid

Washing and eyewash facilities must be available near areas where mercury contamination might be present. All workers must know how and when to use these facilities. Soap and water should be available at these facilities to treat contaminated skin.

Eye exposure

If mercury gets into the eyes, irrigate with tempered water for at least 15 minutes. Any affected workers should have an eye examination as soon as possible.

Skin exposure

If mercury gets on the skin, immediately wash the affected area(s) with soap and water. Remove any clothing or jewellery that might have been contaminated and store for cleaning or disposal.


If workers inhale mercury vapour, move them to fresh air and monitor for respiratory distress. Administer oxygen and assist with ventilation if required. Symptoms of pulmonary edema can be delayed up to 48 hours after exposure. Immediately transport workers to an emergency care facility.

Medical monitoring

Where workers are exposed to mercury, biological monitoring (e.g., the collection of blood and/or urine samples) may be necessary. Medical monitoring programs may involve both baseline and periodic examinations and should only be conducted by, or under the supervision of, a physician knowledgeable in occupational medicine.

If you think workers have been exposed to mercury, they should see a physician knowledgeable in work-related health problems.

Workers should report any suspected health effects to their employer and a physician. Workers should act on medical advice and comply with any medical instructions a doctor gives them.

For more information

For more information on mercury, refer to the following web pages:

U.S. Occupational Safety & Health Administration (OSHA), Safety and Health Topics—Mercury http://www.osha.gov/SLTC/mercury/index.html

U.S. National Institute for Occupational Safety and Health (NIOSH), Workplace Safety and Health Topics—Mercury http://www.cdc.gov/niosh/topics/mercury

More Information:

WorkSafeBC has a wide range of health and safety information. For assistance and information on workplace health and safety, call toll-free within BC 1-888-621-SAFE (7233) or visit our web site at WorkSafeBC.com.

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