Earth faults can cause misfires if:

• a borehole is charged several days before initiation
• boreholes are located in fractured rock or where there is a risk of insulation damage
• blasting takes place underwater or in damp environments
• blasting takes place in ore with high electrical conductivity
• ANFO explosives are used.

Prevent earth faults by doing the following:

• Do not place the initiation wire in water.
• Check the earth fault resistance in initiation circuits with an insulation tester. The resistance should exceed four times the resistance of the initiation circuit or be at least 400 ohms.
• Minimise splices on detonator wires in boreholes, and insulate them carefully if necessary.

If a shock-tube system or detonating cord id used, the risk of earth faults is small.

The blasting foreman must inspect the blasted area immediately after the blast, before any other work begins. The purpose of this inspection is to identify any misfires. Locating misfires in blasted rock can be challenging; therefor, the entire workforce must remain alert to their presence.

After a blast, it is also essential to collect any visible detonator leads to ensure that no undetonated detonators remain. If undetonated detonators are found and a manufacturing defect is suspected, the supplier must be informed.

The risk of misfires detonating may persist during subsequent work at the blast site, for example during mechanical cleaning of remaining rock walls, drilling into previously blasted rock beds, or when removing and crushing rock masses.

Develop a clear plan for how misfires will be managed in the workplace. All personnel involved in loading, clearing, drilling, or crushing must be trained to recognise signs of misfires, understand the associated risks, and know how to act if they discover one.

If a misfire is discovered after blasting, it is vital to proceed with extreme caution. The area surrounding the misfire is hazardous and requires careful handling. The first step is to determine the exact location, size, distribution, and content of the misfire. Explosives may have spread into nearby cracks, further increasing the risk. The area of the suspected misfire must be clearly marked.

A misfire may need to be neutralised by a controlled detonation or another safe method, depending on its location and the type of explosive involved. Misfires must only be rendered harmless by qualified personnel, in line with established safety procedures. Only those responsible for neutralising the misfire are permitted to remain in the hazardous area.

If a misfire cannot be rendered harmless immediately, it must be marked and reported so it can be dealt with as quickly as possible. In workplaces with multiple parties, reporting procedures must be clear, and the coordinator or Bas-U must be involved to ensure the process is properly managed.

Misfires that have been safely neutralised may be stored in an approved explosive storage facility.

Large blast rocks can occur during blasting and often present additional challenges, as they may contain misfires.

Large blast rocks typically originate from the upper, uncharged, or pre-charged section of the salvo. They can also result from poor drilling precision, such as when boreholes are spaced too far apart, or from unfavourable geological conditions.

Large rocks must be processed separately from other activities, as there is a risk of both flying stones and explosion of misfires. This is particularly important in large workplaces where multiple activities are taking place simultaneously. When working on the rock with a hydraulic hammer, uncontrolled flyrock can occur, with stones being projected up to 100 metres. Misfires within the rock may also be triggered when fragments strike the ground.

At permanent workplaces such as quarries and rock faces, consider installing permanent protective walls around areas designated for processing large blast rocks.