In order for a control system to be classified as a safety accessory, it shall be designed and placed on the market as an ultimate means of protecting pressure equipment from exceeding allowable limits, and therefore it shall meet the corresponding essential requirements of Annex I, section 2.11.
A measuring system alone cannot be considered as a safety accessory, as a safety accessory as defined in PED necessarily requires
- a measuring or detection function and
- an activation function for correction, or shutdown, or shutdown and lockout.
It is foreseeable that some measuring or control devices could be inadvertently used as safety accessories. Where this is possible manufacturers should include an appropriate warning in their instructions for use.
For example: Quick opening closure on a pressure vessel
A quick opening closure on a pressure vessel is “fitted with a device to prevent it being opened whenever the pressure or temperature of the fluid presents a hazard” in accordance with Annex I Section 2.3. This device is not a safety accessory in acc. to PED ( is not designed to protect pressure equipment against exceeding the allowable limits).
However, there are important safety implications for these devices which are covered by the essential safety requirement Annex I Section 2.3 of the PED. The manufacturer shall address this as part of the hazard analysis. This control equipment could be of a simple self-acting type or of a more complicated type, e.g. with a pressure transmitter and an actuator.
