KANBrief 3/12
In 2007, an accident typical for the sector drew the attention of OSH experts to product standard EN 1953 governing atomizing and spraying equipment: a painter had injected material into his hand by means of an airless spray gun. Accidents of this kind occur repeatedly, above all during cleaning, maintenance and repair work. It was initially unclear whether the accident had been facilitated by a product fault or by inadequate safety measures specified in the standard.
Operating pressures in the airless process are usually between 50 and 500 bar, and less commonly up to 1,000 bar. Atomization is brought about solely by means of the rapid pressure drop at the tip of the gun, without the otherwise usual air assistance. The accident occurred when the painter began changing the tip. The gun was connected by a hose to the material feed. As he was replacing the tip, the worker inadvertently actuated the trigger, shooting coating material into the ball of his other hand. The consequences of such an accident are serious, as the chemicals in the coating materials can rapidly cause the wound to become infected.
Identifying the causes of accidents...
The instruction handbook clearly states that spray guns must not be under pressure during cleaning and maintenance work. On the device causing this accident however, the tip guard, which is intended to prevent precisely this type of accident, was also missing. In the view of the former "Metal and surface treatment" expert committee of the BG for the woodworking and metalworking industries (BGHM), the failure to observe these requirements was ultimately the primary cause of the accident. Both requirements are however stated in the existing standard.
Conversely, the Regional Centre for Occupational Health and Safety (LAfA) of North Rhine- Westphalia initially concluded that inadequate safety provisions in EN 1953 were the cause of the accident: in the Centre's view, a spray gun presenting such a high hazard potential should be interlocked automatically when switched off. This logically resulted in a formal objection to the product standard being proposed. In fact, virtually all airless spray guns provide protection against inadvertent actuation by means of an interlocking device which must be operated manually, as required by the standard. This device is used during breaks between spraying, and for cleaning and maintenance work. Automatic interlocking when the trigger is released – which is in fact a plausible protective measure – is not required by the standard. Why is this the case?
... and the appropriate protective measures
The pros and cons of automatic interlocks have been a subject of discussion for as long as the regulations governing high-pressure spray guns and other fluid spray equipment have existed. One major argument against is that almost all coating work is performed with interruptions, and the spray gun must therefore be continually switched on and off. Each spray operation lasts only seconds or fractions of a second. An automatic interlock would involve significantly more effort on the part of the sprayer, who would have to release the interlock each time before resuming spraying. A predictable consequence would be that interlocks would be defeated, resulting in modified devices presenting an even greater hazard.
KAN chairs meeting of experts
In order for the different viewpoints to be channelled and for a consensus to be reached between the expert opinions, the Federal Ministry of Labour and Social Affairs ultimately brought in KAN. The essential results of the meeting of experts that was convened are as follows. The causes of the accident were the missing tip guard and the replacement of the spray tip under pressure. Certain improvements to EN 1953 were nevertheless considered warranted, including the following:
The "new" EN 1953
The result of the meeting of experts formed the basis and starting-point for the revision, which was in any case pending, of EN 1953, publication of which dated back to 1998. The responsible Working Group 2 of CEN/TC 271, "Surface treatment equipment – Safety", submitted the draft to the public enquiry process in May 2012. A number of further requirements set out in the standard were reformulated/specified in order to improve the safety of products from all manufacturers. The new version of EN 1953 is expected to be published by the end of 2012.
Roland Knopp