Posted By John Webster
I would have thought this one came down to risk assessment. Ask the "what if" question. Is anybody at risk if the operator looses grip of the machine? What safeguards are in place if the machine jams or snags? Try to imagine both the probable, and the just possible. Talk to users. They may have experiences of near misses.

About 20 years ago I was using a large, low speed power drill to bore a hole in steel work. The bit jammed. The drill continued to rotate in my hand and wrenched from my grip. The trigger had a locking button which became depressed as the handle twisted around, so the drill did not stop and wound the cable arould my arm, tying it to the drill. Only the quick reaction of a workmate in killing the power at the socket saved me from serious injury.

So I may be biased, but I will not use any power tool without an effective and non-bypassable "dead-man" mechanism unless there are other design features which will guarantee safety.

Posted By Calum R Cameron Tech SP AIIRSM
As a general reponse I would have to say that without specific requirements in PUWER 98 the answer lies in HASAWA s2.2 where there is a requirement for an employer to provide safe plant.
Therefore, with this in mind, is the lockable trigger going to put the user at greater risk than a tool without a lockable trigger.
If the tool does not have a torque limiting clutch then the risk is likely to be higher on a tool with a locking trigger mechanism.
The financial implications of altering the trigger mechanism are probably minimal and therefore you would probably not be supplying plant which is safe (so far as is reasonably practicable)if it was supplied with locking triggers.
The results could be prosecution by the HSE and/or a civil case brought by the injued or mamed employee.
Hope this of assistance and please don`t hesitate to contact me if you want anymore assistance.

Posted By Kevin Minton
Jinm & other readers

There are other considerations:

The extract from the European Standard is not quite complete. Section 20.11.1 states:
"Where there is a risk associated with continued operation, the switch shall not have any locking device to lock it in the ON position and it shall not remain in the ON position when the trigger is released. This shall be stated in the relevant part 2".

I understand this to mean that where the technical committees identified this as a risk, they state so in the part that refers to specific requirements for that class of tool.

For drills, 50144-2-1:1999 is silent on this point. It specifies other means to limit excess torque.

For angle grinders, as far as I am aware, EN50144-2-3 is not yet published.

I recall that the old BS2769 part on angle grinders allowed lock-on switches on smaller grinders (up to 6" ?) but disallowed them on 9" and larger grinders.

Discussing this point with an experienced enforcement officer a few years ago, it became clear that recorded relevant accidents with angle grinders all involved the switch having been scotched - that is, permanently fixed in the ON position with tape.

The risks of operators cheating switches to ON is high because they get fatigued holding it on. The resultant risks then include no emergency stop in any form.

Inspection of bigger grinders from reputable maunfacturers show that they have switches easy to knock off. Their risk assessments have evidently pointed to this as the best overall solution.

I hope this adds to the debate!

Kevin Minton