In this article, the editor of Pilz Safety Update news interviews Ian Murgatroyd, one of the Pilz engineers trained in ESPE certification.
Editor: What is ESPE certification?
IM: ESPE stands for electrosensitive protective equipment and is the technical term covering safety light curtains. The certification process involves an inspection to ensure that the light curtain cannot be defeated and that it is correctly positioned in relation to the mechanical hazards. Note that sometimes people refer to AOPD (active opto-electronic protective device) certification, which is the same as ESPE certification.
Editor: Why is ESPE certification necessary?
IM: The Provision and Use of Work Equipment Regulations 1998 (also known as PUWER 98) state that safety-related equipment must be inspected to ensure it is 'suitable and sufficient' for the intended purpose and that any equipment that might degrade over time should be inspected regularly. Most suppliers of light curtains also state in their documentation that there should be regular inspections. In this context, 'regular' is normally interpreted as 'annual'.
Editor: So is ESPE certification only applicable to existing machinery?
IM: No. Some machine builders like to have the added peace-of-mind that comes from an independent ESPE inspection, and people upgrading older machines by installing safety light curtains often like to have an independent assessment. But the majority of ESPE certifications will be on existing machines.
Editor: How long does it take to complete the certification process, and what is involved?
IM: To certify a machine that has one safety light curtain would take about an hour, plus a little more time to complete the documentation. The guiding principles behind the assessments are laid down in IEC 62046 (Technical Specification, Safety of machinery – Application of protective equipment to detect the presence of persons).
The first things we check are the height of the hazard window, the size of light guard and its type, to make sure the guard adequately covers the hazard window. Then we mount a stop time performance monitor on the machine to check how long it takes for the moving parts to come to standstill from the moment the light barrier is triggered. This figure is used to calculate how far away from the hazard the light guard should be mounted (as per BS EN 999:1999, Safety of machinery, The positioning of protective equipment in respect of approach speeds of parts of the human body). Next we measure the actual distance and compare it with the calculated figure to ensure the light guard has been mounted in the right position. The light guard is then checked to ensure it is correctly integrated within a suitable safety-related control system.
For every machine we compile a written report that includes digital photographs. Provided all the tests are passed OK, a label is applied to the machine to show that it is certified and that it is due for inspection again in 12 months' time.
Editor: Aside from the safety issues, are there any other benefits from having safety light curtain installations assessed?
IM: Obviously you do not want the light curtain to be too close to the machine, as the safety-related control system may not be able to react fast enough to stop the machine in time. But having it too far from the machine wastes floorspace and increases cycle time unnecessarily. So light curtain assessments can be used as part of a plant optimisation process to help improve productivity.