Can someone tell me what the requirements of dorgards are please, these are designed to listen for the audible fire alarm i know but what happens if the fire alarm fails? should these devises be wired in to the electric mains and close automatically? I come across a lot of these that are not wired directly to the system

The dorgard by its design is a standalone unit, so even if you wanted to you can not connect it to anything else.

 

You need to read "BS 7273-4:2015 Code of Practice for the operation of fire protection measures - Part 4: Actuation of release mechanisms for doors." which covers these devices.

Devices that hold open fire doors are divided into different categories depending on their method of operation and intended usage: Critical, Standard & Indirect (used to be category A, B & C).

Dorgard don't state what level their devices meet (they say 'normal' which doesn't exist) but the basic models appear more like Indirect models.

Risk assessment determines which type to use, but considering the reliability of correctly installed, tested and maintained fire alarm systems would rather have loads of Indirect acoustic devices than wedges, disconnected closers etc which were far more prevalent before these were invented. There will be some circumstances where direct wired equipment is required, although to get the most advantage of these they need to be linked to fire alarm systems capable of causing release on fault as well as fire.

Anthony is correct, This is no such thing as a "normal" category. Dorgard qualifies as a "standard" category device according to BS:7273-4. It seems Fireco have updated the website to reflect this. Maybe they saw your comment Anthony.

In situations that require a "Critical" category installation, There is a version of Dorgard which can be wired into the fire panel called Dorgard Pro -  that meets these requirements.