Fire Engineering Glossary

Cause and effect matrix

The site-specific document mapping every alarm input to its required outputs (sounders, dampers, doors, plant, signalling); the reference for commissioning and testing.

An unversioned or missing matrix is a defect worth reporting in its own right.

Commissioning

The systematic proving of a completed installation against the design: device tests, cause-and-effect verification, sound levels, battery calculations and documentation.

Double knock

Cause-and-effect logic requiring a second confirming trigger (same or second device) before a critical output such as plant shutdown or release operates.

Interface unit

A monitored input/output device connecting the fire system to other building systems — plant, dampers, lifts, security — under cause-and-effect control.

Optical smoke detector

A point detector sensing light scattered by smoke particles in its chamber; effective on smouldering fires, more prone to dust and steam nuisance alarms.

Phased evacuation

An evacuation strategy where areas evacuate in stages rather than simultaneously, driven by the cause-and-effect programme and voice alarm or staged signals.