Explosives safety alert no. 93 | 06 December 2021 | Version 3

Safety distance for fan cakes

What happened?

A spectator was injured after being struck by projected debris from a “fan cake” firework during a recent fireworks display. Serious harm may have resulted if the object had struck a more vulnerable area of the spectator’s body. The spectator was located outside the exclusion zone implemented by the fireworks operator for the display.

How did it happen?

The spectator was struck by an object, likely debris, from a projected “fan cake” firework. The object had sufficient energy to travel the distance from the fan cake to the spectator, strike the spectator and cause an injury.

Evidence suggests that the safety distances applied by the operator did not take into account the increased projection distances from the angled side tubes of the fan cake(s) which led to an insufficiently large exclusion zone.

Figure 1 - Example of fan cakes used during fireworks displays showing angled projection of fireworks from launch tubes

Key issues

Existing safety distance calculations DO NOT consider the horizontal projection risks from fan cakes.

Safety distances and exclusion zones are currently based on the vertical projection of fireworks.  However, some fireworks are projected at an angle from the vertical and the increased horizontal distance must be applied to the calculation of safety distances and spectator exclusion zones.

The potentially increased horizontal distance achieved by projections from fan cakes is modelled in Figure 3.

Figure 2 - Fan cake launch tubes prior to loading

Figure 3 - Potential fan cake projection and debris trajectories

Risk factors affecting the safety distances from fan cakes include:

• potentially significantly greater horizontal projection distances from the angled tubes of fan cakes,
• secondary debris from the firework such as clay and plastic plugs used in their construction
• whether the fireworks involve secondary breaks, and
• environmental factors including the presence of strong winds.

Recommendations

The incident investigation found that the risk factor represented by the greater horizontal projection distance from the angled launch tubes of fan cakes has not been mitigated to an acceptable level of risk by the minimum clearance distance calculations contained in the Queensland Outdoor Fireworks Code of Practice (the Code). Minimum clearance distances for fan cakes are not considered or included in the Code.

The investigation recommended an increase in the minimum clearance distance from the angled side of fan cakes as a reasonable precaution to prevent further injury to spectators. Until further information can be obtained from manufacturers or a testing programme, at least a 50% increase in minimum clearance distance to the side of fan cakes was recommended.

Direction

From 6 December 2021, the following direction applies to the calculation of minimum clearance distances (and hence the exclusion zone) in the Code for fan cakes. The calculation remains based on one metre per millimetre of the internal diameter of the firework launch tube.

Direction - increased minimum clearance distances for fan cakes

The minimum clearance distance from the front and rear of a fan cake remains at least twice (2x) the internal diameter of the firework launch tube in metres (1mm x 2 = 2m).

The minimum clearance distance from the sides of a fan cake is increased to at least three times (3x) the internal diameter of the launch tube in metres (1mm x 3 = 3m).

As stated in the Code, an additional 10m is added to the clearance distance to provide the exclusion zone.

Note: If the manufacturer’s recommended minimum clearance distance for an item exceeds the least distances mandated in this Safety Alert, then the manufacturer’s recommended distance is to be used.

Application of direction

Where an exclusion zone is provided with the item by the supplier and is known by the operator, this distance is to be established for firing the firework.

Where that distance is not provided or is not known by the operator the following calculation is to be applied when setting the exclusion zone.

Figure 4 - Calculation of minimum clearance distance for fan cakes

Figure 5 – Worked example for 28mm firework fan cake