How to deal with escape routes and entrapment in safeguarded areas
Emergency release and Escape release are functions that are provided in many different safety switches. However, machine safety documentation that describes product features rarely mentions the need for escape routes or the impact of triggering a stop command.
A frequently asked question when a machine safety systems gets designed is, “Should I allow operators to exit the safeguarded area through a locked access door?”. The answer to this is described in ISO14119 (2013). Using interlocking devices with guards – Design and selection requirements. However, to determine whether this is indeed required, it is necessary to consider the guideline for Risk Assessment and Risk Reduction ISO12100 (2010) – General requirements for design. Risk assessment and risk reduction specify the ground rules, principles and methodology for achieving safety in the design of machinery. This standard is useful because it guides the reader through the risk assessment process and a selection of safeguarding methods. Section 220.127.116.11. – Measures for escape and rescue of trapped persons – is the relevant section when the risk analysis shows that there is a risk that an employee could become trapped in a guarded area when using controlled access (lockable safety switches). In this scenario, an employee should be able to leave the zone in the event of a calamity or unintentional machine start. There is also the possibility that employees have to leave the room via another access point then how they have entered, such as in the event of a fire.
The use of personal safety keys (keys released from a safety switch with a safety key function) can be used to reduce the risk of workers becoming trapped in a safeguarded area and to prevent accidental machine startups. ISO / TS 19837 (2018) “Key Lock Systems” describes this extensively and clarifies where private keys cannot be used as an alternative to an additional unlock. In particular, the examples described here are very helpful in determining the need.
Once the requirements for an escape route have been established, the type of exit that must be used can be determined based on ISO14119 (2013). In Section 5.7.5 – Additional unlocking of interlocks – the three types of exits are described as:
- Escape release
Unlocking from the inside of the safeguarded area without the need for tools.
- Emergency release
Unlocking from the outside of the safeguarded area without the need for tools.
- Auxillery release
Unlocking from the outside of the safeguarded area, requires special tools.
In all of the above cases, actuation generates a stop command. The full requirements are described in section 5.7.5. It is important to mention that unlocking is a manual action that intervenes directly with the locking mechanism in case of an emergency or escape release.
In reality, there is, sometimes, still a lack of clarity about the difference between escape release and emergency release. Escape release is by far the most widely used, but there are instances where an emergency release should be used. An example is when a production line operator becomes unwell in a location with some distance from the open-access door and when access must be gained through another access door where an interlock is installed. An emergency release in the form of an override button can provide a solution.
Another risk that is sometimes overlooked when considering additional locking of the unlock safety device is the system ramp-down time. This is because the operation of the escape, emergency or auxiliary release gives direct access to the hazard, regardless of the time it takes the machine to come to a stop, and this must be taken into account during the risk assessment, as the hazards of moving machine parts are still are always present.
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