The standard that should be followed for the safe operation of palletisers is EN 415-4: Palletisers and Depalletisers. Clause 3 of the standard describes the different types of palletiser and depalletiser covered and includes isometric drawings to illustrate how each machine works, as well as defining the terminology used for such machines.
The Health and Safety Executive (HSE) also outlines safety principles for palletisers and depalletisers, which state that danger zones must be protected, including the guarding of machine entry or exit points, with methods such as interlocking moveable guards, captive key exchange systems or electro-sensitive protection equipment (ESPE), such as light curtains.
Limiting access
Due to the size of palletisers, most injuries happen when people enter the machine, for maintenance or if there is a problem with it, and they end up being trapped between its many parts. This means that personnel can be in the machinery without the knowledge of those outside and it might be re-started, with severe consequences.
One example from HSE is from within the food manufacturing industry where an engineer suffered fatal crushing injuries when working within the danger area of a large robotic palletising machine. The machine started up unexpectedly, as it had not been electrically isolated and the power locked off. According to HSE, in food and drink manufacturing alone around one fatality a year results from workers entering large machines.
Light curtains are opto-electronic guarding devices used to protect personnel. Many assume that operators are fully protected by these systems, but they are often positioned incorrectly and consequently deliver no safety benefit at all. This is often because the positioning and detection capabilities of the light curtain are not optimised, as they tend to be positioned to detect the pallet, rather than the pallet load.
This means that the gap between the light curtain and the pallet load is too large, which allows people to get in when the machine is not operating.
As palletisers transport a heavy and bulky load, operators are also exposed to potential hazards from loads falling off the moving pallets. It is therefore essential that, where physical guards are used, they are of the correct dimensions to stop people getting under or over them. In this case, the height of guards must be selected using Table 2 of EN ISO 13857 ‘Safety of machinery - Safety distances to prevent hazard zones being reached by upper and lower limbs’.
Clause 5.3.2 of EN 415-4 states that the entry and exit point for people should be different from the entry or exit points for pallets. The HSE suggests that, typically this will be a guard door interlocked with a device complying with EN 1088. If the operator uses the guard door, it is clear that someone has entered the machine through the open door, whereas if they were to enter through an ESPE, there is no visual clue that they are inside.
Clause 5.3.3 states that, after a person has entered a machine, it must only be possible to reset and restart a palletiser or depalletiser by a deliberate action on a device located outside of the danger zone, in a position where the person operating the device has a clear view of the danger zone. The HSE points out that, on some large machines where it is not possible to see all of the inside of the machine from a single position, it may be necessary to have more than one device to comply with this requirement.
One option to improve safety at entry/exit points is to use a Captive Key Exchange system, where a mechanical key must be removed to isolate the machine and release another key, which the person takes into the machine with them. The machinery cannot be re-started until that key is returned.
Plants often fail to fit appropriate infill panels between conveyor rollers. This is a requirement within EN 415 -4, in order to prevent trapping and crushing between the pallet and the roller.
Standard updates
EN 415-4 was originally published in 1997 by CEN, the European Committee for Standardisation. However, in 2006 a decision was taken to completely revise the standard, taking into account changes in machinery technology, such as the increasingly widespread use of industrial robots.
CEN’s aim was to publish the revised version of EN 415-4 by 2011, but more than a decade later it is still under development. This means that technically there is no standard for palletisers and depalletisers on the latest listing for the Machinery Directive published in the Official Journal of the European Union.
If any accidents or injuries are caused by palletisers, machinery owners could be prosecuted under the Provision and Use of Work Equipment Regulations (PUWER), or machinery suppliers prosecuted under the Supply of Machinery Regulations, which relates to CE marking requirements.
TÜV SÜD’s advice is to continue using EN 415-4 until its revision is eventually published, as this approach indicates ‘best practice’ and shows due diligence on the part of the machinery owner.
However, the failures we see on site are often due to a lack of appropriate internal expertise and physical resource to do an in-depth and correct PUWER assessment of all machinery. As palletiser machinery is so large and complex, the matter of time and expertise availability becomes an even greater issue.
Despite this, a thorough PUWER assessment should be completed before any new machinery goes into operation. Problems can then be rectified with the manufacturer, so that they or the machinery owner no longer run the risk of a prosecution under the Machinery Directive or PUWER. A decision to ‘make do’ or not invest in the appropriate expertise to run PUWER assessments on palletiser and depalletiser machinery could prove fatal – the HSE statistics prove that.