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Jargon Buster

Letter H

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Hold-back (also known as dogging) allows the latch and/or bolts of an exit device to be held in the withdrawn or open position.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.

The hold-back feature was designed for fire exit doors and should not be used on an internal fire door unless the door has been certified as a fire door with unlatched hardware.

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.


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

Some RF products can transmit and receive signals over 150 metres (in free space) so it is important to ensure neighbouring systems do not interfere with your system and vice versa. After carrying out the house coding procedure, the alarms and the remote control will only communicate with other units house coded at the same time. The information for house coding radio-interlinked units can be found in the user manual.