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Chemical reaction exposes worker to toxic gas

In March 2022, a worker was seriously injured after being exposed to a toxic gas following a chemical reaction in a pump shed. Initial enquiries indicate the man was using a drum pump to deliver sodium hypochlorite inadvertently into a tank containing sulphuric acid as part of a water treatment process. As a result of the two chemicals reacting, a toxic gas was generated. It escaped through an unsealed opening on the tank into the work area.

Investigations are continuing.

Safety issues

Some of the chemicals used in the treatment of water supplies treatment facility or swimming are incompatible with each other. That is, when brought together, they react dangerously. An example is the reaction between chlorine-based products (e.g. sodium hypochlorite) and acids (e.g. hydrochloric or sulphuric acid) which releases toxic and corrosive chlorine gas. Care must be taken to avoid mixing such incompatible chemicals.

Processes or conditions in which incompatible chemicals have the potential to come in contact with one another include but are not limited to:

  • dispensing or transferring of different chemicals using a “common” container
  • using contaminated or improperly labelled containers, transfer lines, or piping
  • spills or leaks of different chemicals kept within a common spill containment system or compound.

Ways to manage health and safety

Taking steps to manage risks is a condition of doing business in Queensland. Effective risk management starts with a commitment to health and safety from those who manage the business. If an incident occurs, you'll need to show the regulator that you’ve used an effective risk management process. This responsibility is covered by your primary duty of care in the Work Health and Safety Act 2011.

Use the hierarchy of controls to help decide how to eliminate and reduce risks in your place of work. The hierarchy of controls ranks types of control methods from the highest level of protection and reliability to the lowest. It’s a step-by-step approach to eliminating or reducing risks. You must work through the hierarchy of controls when managing risks, with the aim of eliminating the hazard, which is the most effective control.

Possible control measures to prevent similar incidents

The Work Health and Safety Regulation 2011 includes a number of duties for a person conducting a business or undertaking (PCBU) in order to manage the risks to health and safety associated with using, handling and storing hazardous chemicals at a workplace. In addition, specific sections of the WHS Regulation require the PCBU to identify any risk of a physical or chemical reaction in relation to a hazardous chemicals used, handled, generated or stored at a workplace.

Upon considering the risks involved with the handling, use or storage of specific hazardous chemicals, an assessment of the chemical hazards, task hazards or nature of work and the work environment is required. This consists of but is not limited to:

  • reviewing the container labels and Safety Data Sheets (SDS) for the hazardous chemicals and assessing the information provided on the safe storage, handling and use
  • deciding whether the hazardous chemicals risk in the workplace is adequately controlled with existing control measures, as recommended in the SDS and other reliable sources such as relevant Australian Standards, Codes of Practice, manufacturers guidance and related incident data and reports
  • implementing additional control measures to address any identified gaps
  • ensuring risk controls are maintained and periodically reviewed.

The SDS assists this assessment by providing critical information about hazardous chemicals including:

  • health and physical hazards
  • safe handling and storage procedures
  • situations that may generate hazardous chemicals
  • emergency procedures
  • disposal considerations.

The risk of bringing two or more incompatible hazardous chemicals in contact during the transfer or dispensing process can be eliminated or minimised using controls such as:

  • ensuring containers, pipework and equipment are free from contamination, particularly from an incompatible hazardous chemical
  • ensuring transfer fittings are compatible and dedicated transfer lines are used rather than shared or common lines
  • ensuring containers and pipework are correctly labelled so contents are readily identifiable
  • isolating (or segregating) incompatible hazardous chemicals from each other (this can be done by distance, barriers, or a combination of both)
  • installing overflow protection on equipment and receiving vessels
  • providing emergency shut-offs to limit the amount of hazardous chemical released during a loss of containment
  • providing a spill containment system/s, where incompatible chemicals will not be brought into contact with one another
  • maintaining a safe atmosphere in the storage and handling area using a ventilation system (the most appropriate system should be designed in accordance with appropriate technical standards, and installed and maintained by qualified or experienced persons, such as engineers or occupational hygienists)
  • installing plumbed eye wash stations and safety showers in areas where workers may be exposed should there be a spill during transfer
  • designing and implementing planned maintenance programs for chemical handling systems that should be carried out at regular intervals, consistent with the manufacturer’s instructions or advice provided by other competent persons (for example; checking for signs of corrosion or degradation on tanks and pipe work.

Administrative controls should only be considered when other higher order control measures are not practicable, or are to support other control measures. This could include, but is not limited to the following examples:

  • developing policies and safe work procedures for the use, handling, storage, clean up and disposal of hazardous chemicals (for example, tank filling instructions, spill clean-up and emergency procedures)
  • providing easy to understand information, training and instruction to workers
  • obtaining the current safety data sheet (SDS) from the manufacturer, importer or supplier of the chemical and making the SDS readily available to workers
  • prepare a register of hazardous chemicals at the workplace and keep it up to date (the register must be readily accessible to workers involved in using, handling or storing hazardous chemicals and to anyone else who is likely to be affected by a hazardous chemical at the workplace).

In most circumstances, personal protective equipment (PPE) such as overalls, aprons, footwear, gloves, chemical resistant glasses, face shields and respiratory protection should not be relied on to control risk. It should only be used when all other reasonably practicable control measures have been used and the risk has not been eliminated, or as interim protection until higher level controls are implemented.

The control measures you put in place should be reviewed regularly to ensure they are effective.

More information

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