During the firing of a quarry production shot, fly rock ejected from the blast travelled several hundred metres and entered a neighbouring property. Several rock fragments struck and damaged buildings. These fragments narrowly missed employees who were actively working on the property at the time of the shot fire.
Figure 1: Damage to façade resulting from fly rock impact.
Figure 2: Large fragment of fly rock, 30cm ruler for scale.
Mining and quarrying are high-risk activities. Misfires and fly rock are common hazards associated with shot firing activities, which are routinely undertaken in these industries.
Employers and other duty holders who fail to adequately identify and control the risks associated shot firing activities can create serious risks to the health and safety of both employees and people in the surrounding areas.
To reduce the risks associated with shot firing activities, duty holders must:
- ensure a blast management plan is prepared for any work that involves the use of explosive blasting
- ensure shot firing activities are always planned and conducted by a competent and qualified person
- perform a risk assessment to identify all potential hazards, including the potential for fly rock generation, and assess the adequacy of all considered control measures such as exclusion zone extents and pre-shot clearance
Other recommended ways to control risks
- identify nearby infrastructure (sensitive receptors) and determine if adjustments to the blast design are necessary to avoid impacts
- verify that the first row of drilled blast holes have adequate burden in relation to the free face of the shot, this is particularly important for angled holes with variable free face profiles
- prior to firing the shot, check that the stemming height, first row burden and powder factor(s) are within acceptable design limits
Duty holders should also ensure that the result of each shot is recorded (including video) and used to assist in both reviewing the adequacy of controls and to aid in planning future shots.
Under the Occupational Health and Safety Act 2004, employers must, so far as is reasonably practicable:
- provide and maintain a working environment that is safe and without risks to the health of employees and independent contractors
- provide employees with the necessary information, instruction, training or supervision to enable them to do their work in a way that is safe and without risks to health
- ensure that persons other than employees of the employer are not exposed to risks to their health or safety from the conduct of the undertaking of the employer
In addition, under the Dangerous Goods (Explosives) Regulations 2011, shot firers must not use explosives unless the shot firer has first prepared a Blast Management Plan in accordance with the applicable requirements of AS 2187.2.