Mobile crushers are used in a wide range of industries, including quarrying, ore processing and recycling of demolition waste. This guidance is for all those with responsibilities for the operation of mobile crushers, including contract managers, supervisory staff and operators of these machines. It covers the safe operation of the mobile crushing operation and includes guidance on clearing blocked crushers.
This guidance cannot cover every risk and is not comprehensive. It does not attempt to detail individual machinery safety concerns, but will only highlight those key matters of concern.
The risks associated with your particular operation, and the methods of reducing those risks, should be revealed during your risk assessment.
Mobile crushers are versatile pieces of equipment with many uses. A properly planned operation will be efficient, safe and productive. A poorly planned operation will be unproductive, dangerous and inefficient.
These machines can, and have, killed.
Mobile crushers will normally be fed from loading shovels, backhoe excavators or from other processing machinery (e.g. sizer/separator, elevating conveyor, etc).
In its simplest form it will be a standalone machine, fed directly with the material to be crushed and discharging to a stockpile ( see Fig 1 ).
If the material to be crushed is reinforced concrete, then generally a magnetic separator will often be positioned over the discharge conveyor to remove the metal and prevent it from contaminating the production run material.
Fig. 1 Typical mobile stone crusher
If the mobile crusher is to be fed directly by a loading shovel or excavator, then:
If the crusher is to be fed directly by a conveyor:
Fig. 2 Excavator feeding mobile stone crusher
Causes of crusher blockages can be grouped under two main headings:
Working on the premise that prevention is better than cure, every effort should be made to prevent oversize material or tramp metal entering into the crusher feed hopper by:
A properly designed mobile crushing operation should not need any person to be present on the crusher access platform during normal crushing operations.
Being on the access platform during normal operation presents the following risks:
It may be necessary for a person equipped with the appropriate PPE (e.g. ear defenders, dust mask, eye protection, hard hat, protective footwear, high visibility outer garment) to spend a few minutes setting the feed speed initially if there is no remote facility. The feed should then be controlled from the machine feeding the crusher by varying the loading rate into the feed hopper.
Hazards encountered may be:
The preferred method of clearing a bridged crusher is by the use of a hydraulic arm (typically a360 excavator fitted with a quick hitch bucket attachment and either a static pick or a hydraulic hammer available).
Depending on the result of your risk assessment, clearing out a bridging blockage with a hydraulic arm (with pick attachment) may be carried out with or without the crusher still operating.
Use of cranes (including manually operated lifting tackle), Lifting and Slinging
When hydraulic arms are not available and cranes slung with hooks have proved ineffectual, other methods are necessary. When it becomes necessary for a person to enter the crusher to position hooks or slings, the crusher and feeder must be stopped, isolated and locked off (in accordance with manufacturers/suppliers instructions) and safety harness worn.
Where other options are to be considered they should be subject to a detailed and thorough risk assessment. The crusher should be shut off and isolated before considering the use of bars and hand hammers. Careful consideration should be given to the risk of large pieces of feed material moving and causing trap or crush injuries. Wedges should not be used due to the risk of them becoming a projectile (This has caused fatalities in the past). Other options, which require more specialist expertise and competence, include: gas or chemical expansion, hydraulic ramp plates, permanently mounted hydraulic breaker (may include the use of closed circuit television CCTV to assist the operator), use of explosives.
A stalled crusher should be treated as possibly being jammed with tramp metal, which could be ejected with fatal consequences. Written instructions should be issued to plant operators. This should detail the procedures to follow in the event of a crusher stalling. These instructions should include the following:
If, after careful examination, there appears to be no electrical or mechanical reason why the crusher has stalled, it may indicate that the crusher is jammed by tramp metal.
A "stalled crusher permit to work" system should be implemented. This work should only be carried out by person/s who are suitably trained and competent.
Wherever possible any inspection of the crushing cavity of a jaw crusher should be carried out from below the crusher, not from above.
Fatal accidents (due to material being ejected) have occurred to people who have examined the crushing cavity of a stalled crusher from above.
Inadequate guarding is a major cause of injury. Guarding integrity should be checked at regular intervals, particularly after cleaning or maintenance work.
Keeping clear working areas clear of spillages improves operational efficiency and also reduces the risk of slips and trips – a major cause of lost time accidents.
Minimise spillages by:
Never remove guards to clean up while the machine is in operation. If guards need to be removed, shut off and lock off.
To minimise the transport risks on site, a risk assessment should address:
It is essential where possible to segregate pedestrians from moving plant such as loading shovels, excavators and dump trucks by the use of physical barriers.
More detailed information on Transport can be found in the HSE publications: The Safe Use of Vehicles on Construction Sites HSG 144 - ISBN: 0 7176 1610 X and Workplace Transport Safety Guidance for employers HSG 136 ISBN 017176 HSE Books or on the HSE website