At the site of an oil and gas well, three workers were exposed to highly toxic gases while transferring hydrochloric acid from a tank truck to a vacuum truck. The vacuum truck cargo tank already contained tank bottom sludge from a sour gas site as well as chemical-containing waste water from another well. As the hydrochloric acid mixed with the hazardous waste fluid already in the vacuum truck tank, a chemical reaction occurred. As a result, toxic gas escaped from the vacuum truck discharge vent and likely from its pressure relief valve as well.

One worker experienced dizziness but managed to walk away to safety. However, the other two workers passed out. Only one slowly regained consciousness by himself. The other worker needed first aid to be revived.

Risk of exposure to toxic gases during vacuum truck operations

During vacuum truck operations, workers are at risk of being exposed to toxic gases. The potential for releasing toxic gases exists whenever vacuum trucks suck up liquid waste to be transported to disposal sites. For example, the waste water from oil and gas wells might contain highly toxic gases such as hydrogen sulfide (H2S). Low levels of exposure to H2S can result in symptoms such as eye irritation, sore throat, nausea, and vomiting. At high levels of exposure, workers not wearing the appropriate protective equipment will pass out. Too much of the gas can kill a worker in seconds.

H2S is only one of the toxic gases that may result from vacuum truck operations. Any mixing of liquid waste with other waste products can result in unpredictable chemical reactions that produce other gases just as dangerous as H2S. For example, the hydrochloric acid used at oil and gas sites may react with the waste products already in a tank to release hydrochloric acid fumes. Workers may be exposed to potentially lethal levels of hydrochloric acid fumes if they aren't wearing the appropriate protective equipment.

This bulletin reviews the responsibilities of prime contractors and employers for ensuring safe vacuum truck operations.

Prime contractor and employer responsibilities

Part 23 of the Occupational Health and Safety Regulation sets out the requirements for the operations of the oil and gas industry—including vacuum truck operations. The responsibility for compliance rests not only with the employer of the workers involved in vacuum truck operations but also with the prime contractor at multiple-employer work sites. The following are key points from Part 23 of the Regulation.

At a multiple-employer workplace where overlapping activities may create hazards, the prime contractor must appoint a qualified site safety coordinator. The coordinator's responsibilities include informing all employers about the hazardous products used and produced on site. The coordinator must ensure that employers and workers are aware of the hazards that may arise from overlapping work activities. The coordinator must also ensure that these hazards are adequately addressed during work activities.

Employers are responsible for identifying work activities or circumstances—including the release of toxic gases—that may injure workers. Employers must implement safe work procedures to eliminate or minimize the risk of exposure to toxic gases. In addition to providing safe work procedures, employers are responsible for the training and supervision of workers involved in vacuum truck operations.

Safe work procedures for vacuum truck operations

Safe work procedures for vacuum truck operations must address the potential for chemical reactions and the potential release of toxic gas or fumes. They must also take into account the variety of fluids or substances that vacuum trucks typically carry.

Before starting any vacuum truck operations—

To prevent exposure to toxic gases during transfer operations—

Instruction, training, and supervision of vacuum truck operators

Employers are responsible for properly training, instructing, and supervising workers. These responsibilities include the following:

For a checklist on the safe operation of vacuum trucks and fluid haulers, go to At the top of the home page, click on Safety at Work. Then under the Industries heading, click on Petroleum (Oil and Gas). "Vac Truck and Fluid Hauling Inspection Checklist" will appear under Popular Picks.

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

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