Safety first

The Victorians combined brass and unprotected cogwheels in their great industrial sculptures of machines. But as design has evolved, the emphasis has swung from aesthetics to safety. Colin Carter explains.

Building machines today isn’t the hit-and-miss venture to create a thing of engineering beauty it was in the past. Safety rather than aesthetics rules the design, and we are unlikely to see again industrial sculptures using brass ball governors rotating at high speed at head level.

As technology has evolved, so the need to protect those operating or working around machinery has moved forward. Severe penalties are handed out to companies (and individual company directors under corporate manslaughter legislation) not doing all they can to look after their employees.

As an illustration of the scale of the problem, the Health and Safety Executive reports that in the manufacturing sector in 2004/05 there were 41 fatal injuries, with the number of reported major injuries at 6,078. many more thousands of incidents went unreported. Of course, not all of these were down to poor machine design, but there is, no doubt, room for improvement.

Given this need for safety it is hardly surprising that industrial machinery is subject to a number of standards — with non-conformance attracting enormous legal costs and fines if anything goes wrong. There is a whole raft of legislation coming out of the EU and elsewhere, covering such issues as programmable electronic safety-related systems, programmable electronic control systems and general principles for design.

Staying ahead of the standards game is essential for all machine designers, and a display of competence — including knowledge of all relevant standards — is now mandatory rather than just desirable.

An interesting point was made by Jeff Whiting of Mitsubishi Electric UK, when he highlighted the issues of IEC 61508 — the international standard for electrical, electronic and programmable electronic safety related systems — only being as effective as the people who implement it. ‘There is now evidence that IEC 61508 is doing more harm than good for many companies, because it has been so poorly implemented…it is complex and has not been thoroughly understood,’ he said.

Whiting added: ‘The standard also seeks to acknowledge that safety systems are not often provided as an integral part of a plant or machinery, rather than a discrete add-on, which has proven to be one of the areas of greatest confusion.’

Given this background, what can be done to ensure machinery is safe? The first thing is to undertake a risk assessment of the process and decide what you need to be protecting people from. This can be broadly divided into two areas — safety features designed to prevent things escaping, and those stopping people coming into contact with machinery.

Enclosing machinery completely is one option, but operational and maintenance requirements mean that enclosing only the dangerous elements of the system is often the best way forward. And the hazard may not just be from moving parts — factors such as the escape of gases and fumes, electricity, ionising radiation and high-energy laser emissions all have to be considered.

Another strategy to protect staff is to de-activate machinery automatically in danger zones. So-called ‘electro sensitive protective equipment’ senses the presence of movement by some simple mechanism such as the breaking of a light beam and automatically switches the machine off to remove any hazards.

Automatic switch-off can also be triggered by installing safety gates with relays at appropriate points — once the gate is opened, all machinery is de-activated until people move from the danger areas and the system is reset.

Another safety measure is to have controls that require double-handed operation. For example, if a metal cutting machine needs to be operated with two hands, there is little or no likelihood of hands straying towards cutters.

In addition to manual circuit breakers, automatic devices can be built into machinery. These are set to shut down the power if the current reaches a certain threshold — at a level indicating an open circuit somewhere in the system — in much the same way as domestic residual current devices protecting lawnmower users.

Vibration control is another consideration, especially where machinery contains delicate components — such as electronics — that you don’t want to be shaken apart. Anyone who has had a laptop fall apart with relatively limited mechanical disturbance will vouch for that. And vibration often has a high level of noise associated with it, which can mean the machinery falls foul of yet more legislation.

There is also the possibility that people working near vibrating machinery may be at risk. The HSE highlights the effects, and if a firm doesn’t take the necessary steps to protect operators the consequences could be serious as there are a set of ‘Control of Vibration at Work’ regulations in place.

So how can vibrations be minimised in industrial machines? Put very simply, vibration control essentially involves placing material between the machine and the outside environment to absorb the emitted vibrational energy.

Devices to control this come in various forms. rubber mounts — as pads or springs, for example — as part of an isolation system can effectively decouple vibrations from surroundings. In the case of panel flutter, a well-designed vibration mount could reduce or eliminate the noise. Of course, further isolation can be achieved by mounting the machine on a vibration-absorbing base, such as rubber mats or pads. But it is important to think through a vibration control strategy at the design stage for maximum benefit.

There are, of course, many more aspects of safety in machinery design, but it’s clear that designing to ‘best practice’ principles is essential — for safety, efficiency and legality.