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Jargon Buster

Letter H

Heat Detector

A heat detector is an alternative fire detection device which is designed for use in naturally smoky/dusty environments.

Also see Fixed Temperature Heat Detector | Rate of Rise Heat Detector

HMO Pre Alarm Mode

This facility allows for the sounders to be delayed for up to 2 minutes after the panel displays the fire condition. If the cause of the alarm remains or another device on the same zone activates, then the sounders will trigger.

Hold-Back facillity

Hold-back (also known as dogging) allows the latch and/or bolts of an exit device to be held in the withdrawn or open position. This allows free access through the door from both sides and also prevents the latch or bolts from being damaged if the door should be thrown closed.

Hold-Open Devices

A hold-open device on a door closer allows the door to be set in the open position without the use of a door wedge.

Mechanical hold-open devices are unsuitable for use on fire doors as they do not release the door in the event of a fire. If you wish to use a hold-open device on a fire door it is recommended that you use an electronically controlled model which integrates with the fire alarm system and releases the door when the alarm is activated. Electro-hydraulic hold-open devices also release in the event of a power outage.


For Fire Escape Hood please see Fire Escape Hood

Hose Reel

For Hose Reel please see Fire Hose Reel

Hot-Wire, or Glow-Wire, Test

A test of the battery enclosure of an emergency luminaire. The test is to 850 ⁰C, as specified in BS EN 60598-2-22, whose purpose is to ensure that the battery circuits are adequately protected so that internal circuit faults will not set fire to the luminaire.

House Coding

Radio-interlinked products can be capable of transmitting signals over 150 metres (in free space). House coding is a function designed to ensure that neighbouring systems do not interfere with each other and puts all the interconnected devices on a unique radio frequency.