Functions and applications of protective devices

If the risks cannot be prevented or sufficiently limited by constructive measures, protective devices must be planned and provided in accordance with ISO 12100. A suitable protective device is selected

• either on the basis of a risk assessment for the respective machine
• or in accordance with a machine-specific regulation, e.g. a C-standard

Protective devices should generally allow simple and ergonomic operation of the machine and not obstruct its proper use, both in normal operation and in all life and operating phases. If this is not so in all cases, this can pose an incentive for manipulation and result in a protective device being circumvented. It therefore has only reduced effectiveness with respect to risk reduction.

A fixed guard (e.g. a hard guard) should be used, where the access to the danger zone is not required by the operator during normal operation. If the operation requires more frequent access (more frequent that once per week), ISO 14120 stipulates the use of a moving guard (e.g. door with safety switch) or alternatively electro-sensitive protective equipment (e.g. safety light curtain).

For guards and electro-sensitive protective devices, ISO 12100 generally requires that they

• 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
• Are positioned at a sufficient distance from the danger zone (see ISO 13857 and ISO 13855)
• Must not obstruct the machine operation and the work process more than necessary in order to reduce every incentive for circumvention or manipulation
• 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.

Protective measures therefore usually have a risk-reducing effect because – if applied correctly – they influence one of two risk parameters particularly intensively:

• Risk parameter E (Exposition) as a measure of the probability that a person or part of the body being present, by the protective device preventing persons or parts of the body being inside the danger zone (guards)
• Risk parameter O (Occurrence) as a measure of the probability of a hazardous event occurring, by the protective device ensuring that the approach of persons or parts of the body is reliably detected and the hazardous event is prevented in good time, e.g. by a stop command being triggered by a laser scanner.

Overview of typical protective devices and their areas of application

	Type of protective device	Areas of application and notes
	Fixed guard (e.g. fence, cover)	Where no or very infrequent access to the danger zone is required Protection against injury caused by projected (thrown out) parts, objects. Long lifetime
	Moving guard Without guard interlocking (e.g. door or flap) with safety switch (without guard interlocking)	Closing state of the flap or door is monitored. Access to the machine or danger zone is possible. Can only be used if the stop time of the dangerous movement is shorter than the person's access time.
	Moving guard With guard interlocking (e.g. door or flap with safety locking device)	Closing state of the flap or door is monitored and can only be opened by an electrical unlocking signal.
	Safety light curtains Multiple light beam safety devices Single light beam safety devices	For frequent access to the danger zone and ergonomic operation of machines and systems. Safety distance in accordance with ISO 13855 required. In combination with a muting or gating function, material transport through the protective field is possible.
	Safety laser scanners	Access to the danger zone and ergonomic operation of the machine possible. Flexible adaptation of the protective fields to the danger zone. Safety distance in accordance with ISO 13855 required. Limited use in environments with heavy contamination.
	Safety radar system	Access to the danger zone and ergonomic operation of the machine possible. Flexible adaptation of the protective fields and sensor arrangement to the danger zone. Particularly suitable for use in harsh industrial environments
	Two-hand controls	Both of the operator's hands are required for machine activation; the operator is therefore inherently protected against injuries. Other people nearby are not protected. Safety distance in accordance with ISO 13855 required.
	E-STOP device	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.