Explosives safety alert no. 40 | 25 June 2010 | Version 1

Maintenance work on explosives plant and equipment

What happened?

This alert is to advise of the hazards associated with maintenance work on explosives plant and equipment covering hot and cold work on plant and equipment with hollow sections, including welding and cutting activities.

Scope

This alert provides important safety information for all persons associated with the management of activities for performing hot and cold work maintenance activities on plant and equipment which has been in use with explosives.

Background

A small explosion occurred during a maintenance activity when a horizontal fire screen was being welded to the bottom of an explosives carry box. The section underneath the carry box where the welding was being conducted was an enclosed hollow section. The carry box had been in service for some years.

There were no injuries from the effect of the explosion which was believed to be from the ignition of solvents used in the adhesive within the hollow section. The plywood floor and timber lining from the inside of the carry box was severely damaged and the carry box was distorted.

Image 1 below shows the roof of the carry box after the small explosion. The point of welding was in the corner at the right hand end facing away from the photo.

The horizontal fire screen was being welded to the bottom of the C section on the side of the carry box to the C section on the opposite side. This effectively sealed the bottom of the carry box and any gases that may have been present.

Image 3 below demonstrates the explosive force which ripped the 32mm plywood apart and damaged the internal lining of the carry box.

Issues

Even though the explosion may have been caused from the solvent in the adhesive used to make the box, explosive compounds could have been present. The identification of the hazards and risks from explosives and other hazardous materials present should be carried out prior to any maintenance activity - hot or cold. This is especially important when plant and equipment have hollow sections where explosives and other hazardous materials may accumulate over time.

A permit to work system should be in operation for any maintenance activity for any plant and equipment which has been in use with explosives. Before commencing any maintenance work on any plant or equipment which includes hot work permit or cold work permit systems, the person conducting the permit to work system should check for sealed and hollow sections on the plant and equipment and determine if there are contaminants within these areas that could be explosive.

Whenever maintenance work is planned on plant and equipment associated with explosives during its lifecycle, control measures must be adopted for hot and cold work. Explosives can be initiated by friction, impact, static electricity or heat.

All persons involved in the maintenance and decommissioning of plant and equipment used with explosives should conduct a risk assessment to determine the appropriate controls to be implemented.

Plant and equipment must be decontaminated, refer to Reference A.

Plant and equipment must be rendered free from explosives as a part of the decommissioning and disposal process before disposal, refer to Reference B.

Recommendations

All licence holders should immediately review their safety management system to ensure that maintenance of plant and equipment used with explosives is covered during its entire life cycle. This should include a permit system with a risk assessment process. All licence holders should check that the control measures are in place, the procedures under their safety management systems are being followed and that records are being kept. Ensure that all persons in your organisation receive a copy of this safety alert.

Further Information

More Safety alerts, Information bulletins and reports are available on the Inspectorate's website:

References

A. Safety alert No 03 - Decontamination of explosives equipment prior to maintenance - dated 10 February 1999
B. Safety alert No 26 - Decommissioning and disposal of explosives equipment - dated 20 February 2009