4. Protective devices
4.1 Selecting protective devices
Standard EN ISO 12100 notes on selecting protective devices
If the hazards cannot be prevented or sufficiently limited by constructive measures, protective devices must be planned and provided. The selection of a suitable protective device should be made either in accordance with an existing machine-specific provision, e.g. a European C standard, or on the basis of a risk assessment of the respective machine.
The protective device should generally enable a simple and ergonomic operation of the machine and not obstruct its proper use. If this is not the case this can lead to the protective devices being bypassed in order to achieve an easier operation of the machine.
A fixed guard (e.g. a fence) should be used, where the access to the danger zone is not required by the operator during normal operation. If the operation requires a more frequent access, an electro-sensitive protective equipment (e.g. safety light curtain) or a moveable guard (e.g. doors with safety switches) should be used.
Selecting protective devices: Application advantages – application limits
|Type of protective device||Application advantages||Limits of use|
|Fixed hard guard (e.g. fence, cover)||Long lifetime, protection against injury caused by projected (thrown out) parts, objects||Cannot be used if frequent access to the danger zone is required. More difficult access with maintenance work. Can be removed without being noticed. Safety distance required (EN ISO 13857).|
|Moveable guard without guard interlocking (e.g. doors with flaps) with safety switches (without guard interlocking)||Access to machine is possible. Doors cannot be removed without being noticed.||Protective door can be opened during the operation. Cannot be used if the machine’s stopping time is greater than the person’s access time. Hampers operation when frequent access to the danger zone is required. Safety distance required, EN ISO 13855.|
|Moveable guard with guard interlocking (e.g. door or flap with safety guard interlocking).||The protective door can only be opened with an electric unlocking signal. Prevention of unexpected production interruptions. No safety distance required.||Limited use if frequent access to the danger zone is required.|
|Light beam safety devices, multiple light beam safety devices, safety light curtains||Access and ergonomic operation of the machine possible. Unobstructed material transport through the protective field is possible with combination with a muting function.||Safety distance required EN ISO 13855. No protection against injury caused by projected (thrown out) parts, objects.|
|Safety laser scanners||Access and ergonomic operation of the machine possible. Flexible adjustment of the protective field according to the respective danger zone.||Limited use in environments with heavy dirt build-up. Safety distance required EN ISO 13855. No protection against injury caused by projected (thrown out) parts, objects.|
|Two-hand controls||Location-dependent protective device with control function. Both of the operator's hands are required for machine activation and therefore protected against injuries.||Only protects the person operating the two-hand control device. Other people nearby are not protected. Safety distance required, EN ISO 13855.|
|E‑Stops||Press button(s) for stopping the machine to prevent immediate or threatening hazardous situations.||Additional cautionary measures for emergencies. Not a replacement for other protective measures. The press buttons must be placed within range of the points of operation.|
General requirements for construction of protective devices
EN ISO 12100 "Safety of machinery - Basic concepts, general principles for design - Part 2: Technical principles" contains the following general constructive requirements:
Guards and electrosensitive protective devices
- Must take mechanical and other hazards into account.
- Must be built hard-wearing and robust.
- Must not cause any additional hazards.
- Must not be easily bypassed or made ineffective.
- Must be sufficiently far from the danger zone (see EN ISO 13857 or EN ISO 13855)
- Must not obstruct the machine operation and the work process more than necessary in order to reduce every incentive to go around it.
- Must permit interventions to use or change tools or for maintenance work as much as possible without removing the protective devices. The access here must remain restricted to the area required for the work