Mean machines

Experience has shown that processes like palletising and paper converting can be quite lethal.

Machinery in manufacturing and process industries comes under the scope of the 1998 Provision and Use of Work Equipment Regulations (PUWER) in the UK, and one of the trigger points to carry out a PUWER assessment is when machinery is moved from one place to another.

In the case of one company that had to move operating presses making the sintered material used in brake pads, a PUWER assessment was followed by a risk assessment to engineer out non-compliances using a combination of safety logic and various hardware devices.

The whole exercise was facilitated by the consultancy division of Pilz Automation Technology, which undertakes risk assessments on machines or machine designs in accordance with the requirements of BS EN ISO 12100 : 2010.

The need for simplicity and the preference for an analogue signal is driven by the importance of reliability

Robert Stockham

Each assessment identifies the hazards present, estimates and evaluates the risks, and determines and outlines the measures that may be applied to reduce the risks to acceptable levels.

“We are also active in the food and beverage industries and one specific example involved end-of-line palletising of kegs or bottles for transportation and distribution to supermarkets,” says David Collier, business development manager at Pilz UK.

“This kind of machinery is very hazardous and there are constant fatalities involving their use, so we help several customers who are upgrading palletisers.”

The papermaking process too uses some extraordinarily large machines and is subject to the 2001 Paper and Board Industry Advisory Committee (PABIAC) publication ‘Making paper safely’.

The Committee consists of the paper makers, the Health and Safety Executive (HSE), the trade unions and other interested parties. Since its publication, Pilz Automation has been heavily involved both in the technical committees that advise on the standards for paper making machines and in risk assessments for upgrading machinery.

“There are specific types of paper converting machines called hand-fed platen presses with top and bottom plates,” adds Collier.

“The top plate has a pattern cutting die fixed to it into which the operator places a cardboard sheet and operates the press to bring the bottom plate up to cut the cardboard against the die.

“Some of these machines are up to four metres wide and large enough for people to climb inside in order to put the die into place and to clean swarf out and there have been documented fatalities, so two years ago the HSE issued guidance on how these presses should be upgraded.”

Pilz is now working with the British Standards Institution (BSI) to advise the working group in Europe on how standard platen presses should be updated.

While the moving of machines is a hot topic for the paper and food sectors, other sectors such as petrochemicals, power, and water find trip alarms on compressors and pumps to be a core focus of machine safety.

Rob Stockham, general manager MIE Europe at Moore Industries- Europe, has been involved in several esoteric safety projects like temperature monitoring input trip alarms on bearings for compressors and pumps.

“There is normally some temperature sensor like a thermocouple or resistance temperature detector (RTD) directly wired to a local instrument cabinet with trip amplifiers, or on longer runs there may be a local transmitter to convert the measurement to milliamps for tripping limit alarms,” says Stockham.

“A current loop 4-20mA analogue signal is typically used in safety systems but a digital HART protocol may be added for diagnostics. When it comes to safety, keeping trip loops separate and simple is best for complying with standards, ease of understanding and maintenance.”

The need for simplicity and the preference for an analogue signal is driven by the importance of repeatability when it comes to instrument proof testing, adds Stockham.

“It is simpler to test analogue signal trip levels instead of having to use additional scaling and ranging on calibration data from safety loops,” he says.

“A field transmitter converts signals from thermocouples, RTDs, pressure, flow and level sensors into a 4-20mA signal.”

Physical layer connection

In terms of Foundation Fieldbus and Profibus connection at the physical layer, Moore Industries boasts a number of installations at oil, gas and petrochemical plants with several hundred distributed loops for its intrinsically safe Routemaster system and a patented dual-trunk redundant fieldbus.

In addition to limit alarm trips and switches, the company’s key functional safety range includes SIL 2 and SIL 3 compliant instruments certified to IEC 61508 enhanced by failure modes effects and diagnostic analysis reports.

“We also have diagnostics equipment for HART field devices,” says Stockham. “The advantage of HART is the extra information to make sure instruments are working correctly and to help make decisions about replacing instruments.”