ISO 7240-31:2022

Overview

ISO 7240-31:2022 specifies requirements, performance criteria and test methods for resettable line‑type heat detectors used in fire detection and alarm systems. It applies to detectors where a sensing element is distributed continuously or at short intervals along its length (examples: optical fibre, pneumatic tube, electrical sensor cable) and is connected to a sensor control unit directly or via an interface. The standard covers factory and on‑site assessment, endurance and environmental performance, and also addresses use for local protection of plant and equipment. It explicitly excludes non‑resettable, single‑use fixed‑temperature electrical cables.

Key topics and technical requirements

• Conformance & heat response classes: Defines how detectors are classified by heat response and the conditions for declaring conformity.
• Alarm indication & signalling: Requirements for individual alarm reporting and signalling to control equipment.
• Performance repeatability and reproducibility: Tests and acceptance criteria to ensure consistent operation across units and over time.
• Sensing element behaviour: Fault detection, continuity, and on‑site adjustment of response characteristics.
• Software and interfaces: Requirements for software design, storage of programs/data, and interface modules.
• Environmental & mechanical tests: Procedures for maximum ambient temperature, dry/cold/damp heat, vibration, shock, impact, and corrosion (e.g., SO2) for both sensing elements and control units.
• Electrical resilience: Tests for supply variation, low voltage fault and electromagnetic immunity.
• Fire sensitivity & response: Fire test room methods, static response temperature tests, and response time measurements from application temperatures.
• Test methods and mounting: Detailed test atmospheres, mounting arrangements, tolerances and measurement procedures.

Applications and who uses this standard

• Manufacturers of resettable line‑type heat detectors and sensor control units - for product design, type testing and technical documentation.
• Test laboratories and conformity assessment bodies - to perform the specified environmental, electrical and fire sensitivity tests.
• System integrators and fire safety engineers - to select appropriate detector types and ensure correct installation, interface and alarm behaviour in buildings and industrial sites.
• Building owners, plant operators and regulators - for specifying performance requirements in procurement and compliance with fire safety regulations.

Practical applications include continuous linear detection along cable runs, tunnel and conveyor protection, plant/equipment local protection, and environments where a distributed sensing element (optical fibre, pneumatic tube or electrical cable) is preferred.

Related standards

• Other parts of the ISO 7240 series addressing detectors, control and indicating equipment, and test procedures for fire detection and alarm systems.