A major requirement of the Provision and Use of Work Equipment Regulations (PUWER) 1998 and the associated woodworking Approved Code of Practice (ACoP) is the need to reduce the rundown time of tool spindles by braking.
The safety case is compelling. Woodworking has the worst machinery accident record – nearly twice as many as any other industry – and around 6% of accidents occur during rundown. A further 25-30% happen when the machine is unnecessarily under power. Most tool spindles take more than one minute to stop – some as much as five minutes – which is a disincentive for the operator to switch off and wait for the spindle to come to rest before making adjustments.
Tool spindle braking will therefore reduce accidents on woodworking machines. It will also reduce downtime.
What is required?
The ACoP requires that you fit braking devices when the risk assessment shows that it is necessary – so the issue should be included in your risk assessment required by the Management of Health and Safety at Work Regulations 1999 (TTJ February 10).
The ACoP specifies certain machines where braking is necessary because there is a risk of contact with the tool during rundown. It also states that where they are necessary, brakes should be fitted as soon as possible.
What does ‘as soon as possible’ mean? Clearly it must include the time it takes to do the job and what is technically possible, but for most machines this would be less than three months. However, the ACoP allows at least five years, presumably to spread the economic burden.
The ACoP deadline for fitting brakes to the most dangerous category of machine is December 5, 2003. For the second category the deadline is December 5, 2005; and for those not included in the list it is December 5, 2008. This last category is interesting since it suggests that even if your risk assessment shows that braking is necessary, you do not have to do anything until 2008. That cannot, in principle, be right. Prudent and concerned employers will upgrade machines on the basis of the real risk rather that relying on the ACoP deadline.
Inspectors will expect companies to have prepared a strategy and plan for fitting tool spindle braking by now – and this should be based on the risk, with high-risk and most-used machines done first.
Stopping time
For most machines 10 seconds is considered an acceptable stopping time, although for some large machines, such as resaws and logsaws, the time can be extended to 30-35 seconds where there is doubt about the ability of the machine to withstand the braking forces safely. These times are for normal stopping – not just emergency stopping.
The favoured method of braking for small and medium sized machines is DC injection. The existing motor is retained and a new control box is fitted which injects DC into the AC windings to stop the tool spindle when the stop or emergency button is pressed.
Alternatively you can replace existing motors with one that has an integral brake; or a power-operated mechanical brake.
For existing machines only, you could also fit a manual or foot-operated brake (HSE Woodworking Information Sheet No 38). Logically, therefore, if a machine is fitted with such a brake you need do no more – provided it can stop the machine within the relevant time without undue force. However, this is not sound safety advice. Manual braking relies on the operator using the brake and on the brake being maintained properly. Moreover, as companies fit automatic brakes to some machines but not to others, there is a real risk of operators becoming confused. The best advice is for employers to rely on manual braking in the first instance, but to progressively fit automatic braking as part of the overall plan to make the machines safer. A properly carried out risk assessment should arrive at this conclusion.
No brake required
There are some situations where a brake is not required:
Second-hand machines
In addition, HSE has decided that suppliers of previously-owned machines are not required to fit brakes to machines – even if they are listed in the ACoP – provided they give information to the buyer that the machine needs a brake within the required timescale.
Machine manufacturers or suppliers can provide advice on fitting braking systems and most offer an upgrading service. There are also companies that specialise in braking systems and some have adapted their equipment for woodworking applications.
The typical cost of fitting a braking system to a classical machine is around £400 per motor. Some specialist braking firms have developed multi-point braking systems for machines with several similar-sized motors, but the possibility of using these will depend largely on power requirements and the controls in place for normal stopping.
Contrary to what is stated in HSE Information Sheet No 38, DC braking is possible on slip ring motors. Also, the inference that this form of braking is practical only for small motors (less than 10hp) is equally inaccurate. Motors of 100hp and more have been successfully DC braked. There are two types of motor that cannot be braked by DC injection – commutator motors and DC motors.
Power failure
It is important to recognise that DC injection braking will cease to function in the event of power failure or premature isolation. In some places – particularly schools, colleges and prisons – there is often provision for immediately cutting off electrical power to the whole workshop. Such ‘room emergency switches,’ or incorrect use of the isolator to switch off the machine, means the tool will rundown unbraked. Gibbs Finishing Systems has developed and patented a low-cost method of overcoming this problem by incorporating a power source into DC injection units.
The probability and likely consequences of power failure must be considered in your risk assessment. The introduction of tool spindle braking also carries a requirement to instruct and train machine operators, setters, supervisors and maintenance staff in all aspects relating to its use.
Interlocking
Until now, interlocking has been deemed impractical for woodworking machines in the UK because of the long rundown times. The requirement for tool spindle braking has changed this, and new machinery now has interlocked guards to prevent access to the tools and other dangerous parts while they are in motion.
This should lead to the expectation that existing machines are upgraded to incorporate interlocked guards. It will be interesting to see whether the HSE will enforce this. The day will surely come when a serious accident happens that would have been prevented had the machine been upgraded – and the blame will be laid at the employer’s door. The enforcing authorities should make their position clear on this point.
Essentially there are two types of electrical interlocking. The simplest, appropriate for low risk situations, involves an interlock device that cuts power to the dangerous part, operates the brake whenever the access door or guard is opened, and prevents restart unless the door/guard is closed. For high-risk situations there is the added requirement that the access door/guard is held closed until the tool or dangerous part has come to rest. The choice will depend primarily on the nature of the machine and the reasons for, and frequency of, access. Again, your risk assessment will need to address this.
Any interlocking system must satisfy two rules. First, it should fail to safety so any electrical or mechanical failure renders the machine inoperable. Second, the mechanism must not be easily defeated – a simple plunger-operated switch that is depressed by the guard when closed is not acceptable because this can be defeated easily – and if it fails it usually simulates that the guard is closed whereas in reality it could be open.
On guard
The preferred method of preventing access to a dangerous part of the machine is always a fixed guard – one which is strong, durable and secured by tool-tight connections. Before deciding if a guard needs to be interlocked, consider whether it could be better secured and only removed after the machine is isolated from the power source and within a safe system of work.
However, if access is required regularly then the guard/door will need to be opened easily and interlocking will be appropriate.
