Flammable vapours can linger for much longer than you'd expect, and you need to be aware of them when conducting hot work.

'Hot work' is any process involving grinding, welding, brazing, oxycutting, heat treatment or any other similar process that generates heat or continuous streams of sparks. Undertaking hot work in areas where flammable or combustible chemicals or materials are present, could create a significant risk of fire or explosion.

Conducting hot work on containers such as drums, tanks and pipes that have not been properly decontaminated is a common cause of serious incidents. Even if a drum or container is considered to be empty, and has been empty for a long time, flammable vapours can still remain and be a risk of explosion when heat is applied. Simply rinsing drums or containers is not a fail-safe way to remove oily residues or flammable vapours.

Very small quantities of flammable or combustible substances (including diesel and oils) within a closed drum or fuel tank on which hot work is conducted can have catastrophic impacts. Incidents have occurred where bungs are left in steel drums and containers are sealed/closed off effectively creating a bomb. Heated residues expand and can pressurise the container to the point of failure leading to a significant release of energy that can cause harm to people and property.

Containers of concern are not just fuel containers. Some chemical formulations such as agricultural chemicals may also include flammable or combustible solvents presenting similar fire or explosion risks with their containers.

Fire and explosion can result in catastrophic consequences, causing serious injuries or death of workers and others, as well as significant damage to property. There is real danger when the following elements come together (commonly referred to as the fire triangle):

  • fuel (a flammable or combustible substance)
  • oxygen (usually in the air)
  • ignition (a source of energy sufficient to cause ignition).

Flammable liquids, including petrol, ethanol, enamel paints and thinners, and various solvents, give off hazardous vapours which can ignite if they build-up to their flammable range and come in contact with an ignition source. The risk of these vapours igniting is further increased when working in a confined space, an enclosed area, in a pit, or any other area where natural ventilation is restricted. The hull of a boat is an example of an area where vapours can be trapped and accumulate (concentrate or build up).

Ignition sources can be any energy source that has the potential to ignite a fuel. They can be categorised into four broad types: flames, arcs, sparks and heat. Examples of ignition sources include but are not limited to:

  • naked flames, smoking, pilot lights
  • portable electrical equipment such as power tools, radios, and fans
  • operating equipment with combustion engines such as forklift trucks, generators, compressors
  • hot surfaces, exhaust pipes, hot flues and ducts and frictional heating.
 

Control Measures

The Work Health and Safety Regulation 2011 requires specific controls for prevention of fire and explosion risks associated with hazardous chemicals. These include:

  • s51 - A PCBU a workplace must manage risks to health and safety associated with a hazardous atmosphere at the workplace and;
  • s52 - A PCBU a workplace must manage risks to health and safety associated with an ignition source in a hazardous atmosphere at the workplace.

If there is a possibility of fire or explosion in a hazardous area being caused by an ignition source, as a PCBU, you must ensure the ignition source is not introduced into the area. A PCBU must also manage risks to health and safety associated with a hazardous atmosphere. This includes identifying all sources of ignition, such as welding, hot-cutting, and grinding, which generate heat, flames and sparks, that could cause an ignition.

In relation to hazardous chemicals, a hazardous atmosphere is when the atmosphere has a concentration of flammable vapour that exceeds 5 per cent of the lower flammable explosive limit (LEL) for the vapour.

You must ensure that flammable or combustible substances in the workplace are kept in the lowest practicable quantities. This includes waste liquids in containers and gas cylinders, whether empty or full.

Effective controls for fire and explosion risks associated with hot work are often made up of a combination of controls including:

  • avoiding the reuse of fuel containers and ensuring they are properly disposed of, and
  • isolating fuel sources from ignition sources.


Safe Systems

A safe system of work should be implemented to manage the fire and explosion risks associated with ignition sources and hot work activities. This can include:

  • Having a hot work permit system designed to control when and how hot work is undertaken.
  • Obtaining the current safety data sheet (SDS) from the manufacturer, importer or supplier of the chemical and making the SDS readily available to workers.
  • Ensuring you keep a hazardous chemicals register for use by workers. A hazardous chemicals register is a list of hazardous chemicals stored, handled or used at a workplace – the current SDS for each of the hazardous chemicals listed must be included with the register.
  • Checking what has previously been stored in the empty drum or container by reading the label and reviewing the SDS for the hazardous chemical and assessing the information provided on the safe storage and handling. If it has been found to contain flammable or combustible substances, seek to properly dispose of the container and avoid any hot work on it.
  • Be wary of any container that is not correctly labelled (e.g., label has been removed or has become illegible) or has an unknown history. The best approach is to properly dispose of such containers otherwise it will have to undergo appropriate cleaning and testing to verify that there is no fire or explosion risk resulting from historical contents.
  • If there is no alternative but to perform hot-work on the container, remove all traces of flammable or combustible materials from the container to ensure it is properly cleaned of residues and vapours and certified as vapour-free by a competent person noting that:
    • unless containers have been cleaned out to be free of flammable and combustible substances, vapours can remain in containers for many years, and
    • rinsing drums may not be enough to remove vapours from within a container
  • Using fire resistant barriers to prevent other non-related hot work (e.g. welding or grinding) sparks accidently reaching flammable and combustible materials including nominally empty containers.
  • Do not use drums as a welding or work platform.
  • Store empty drums with bungs removed in a well-ventilated place away from other work areas. Removing the bung will not guarantee all hazardous residues and vapours have been naturally vented. Note that flammable vapours from flammable liquids like petrol are heavier than air and will collect at the bottom of a container and can remain there for years until actively removed.
  • Keeping and maintaining fire-fighting equipment nearby.
  • Providing workers – including experienced workers, with instruction, training, and supervision on the fire and explosion hazards, and safe work procedures. Training should be provided to workers by a competent person with information, training, and instruction provided in an easy-to-understand manner.

  • Ensuring worker training, experience, and competency aligns with the requirements and complexity of the task (workers must be trained and have the appropriate skills to carry out a particular task safely).

    • Keep records of training completed and ensure training is always fit-for-purpose. Some examples might include: How to work safely in hazardous environments, such as confined spaces, hazardous atmospheres, and hazardous areas.
    • How to safely control any fire and explosion hazards if performing hot-work on containers that have contained chemicals.
    • How to access safety data sheets (SDS) for hazardous chemicals and be able to understand key information in the SDS and container labels, and
    • The proper use, storage, and maintenance of personal protective equipment (PPE).

 

For further information, view the WHSQ article on hot work incidents here