Posted By DRB The function of this type of safety devise is dependant upon a number of factors, which include the response time of the machine and the distance between the safety device and the nearest moving part of the machine. The former factor can change as the machine breaking system wears. The latter point can change if the tooling is changed. Given that a lot of these safety related devices are fixed to machines such as press brakes or power presses it would be advisable to have these devices checked annually. The manufacturers will usually provide this service but other companies can as well. In any case reg 5 of PUWER provides for maintenance requirements. It would also be worth talking to your insurance provides who may have in put on this. Feel free to email me direct if you need any further information.