Why RCFM for Tunnels

Personnel cannot enter during a fire · Remote control mandatory · Links to fire detection for auto-activation

System Configuration

RCFM monitors at 50–80 m intervals · Oscillating sector scan per zone · Zone isolation valves

Key Standard

NFPA 502 · Road tunnel · Chapter 10 · Fire suppression system requirements

Chapter 10 — Fire Suppression

NFPA 502 Chapter 10 addresses fire suppression system requirements for road tunnels. Key provisions relevant to automatic fire monitors include:

• ▶Fixed fire suppression systems shall be capable of controlling fire to maintain structural integrity and allow evacuee egress for a sufficient period for emergency responders to enter
• ▶Suppression systems shall be designed to address a single vehicle fire involving the largest hazard vehicle type anticipated in the tunnel
• ▶System activation shall be automatic from fire detection, with manual override available from a remote control station
• ▶Water application rate shall be sufficient to control fire growth and limit temperature rise in the tunnel structure

World Road Association Technical Reports

PIARC (World Road Association) technical reports on tunnel fire safety and suppression systems provide internationally recognised guidance on design fire scenarios, HRR values for different vehicle types, and the evidence base for fixed fire suppression system effectiveness. PIARC Report 2019R02EN is the current reference document for tunnel fire safety. Most national tunnel standards (including those in Europe, Japan, Australia and China) draw from PIARC technical guidance.

China — Fixed Monitor System Code

GB 50338 covers fixed fire monitor system design in China, including tunnel applications. For road tunnel projects in China, GB 50338 §4 together with the tunnel-specific requirements of GB/T 37486 (Technical Specification for Fixed Fire Suppression Systems in Road Tunnels) define the design basis. Both require automatic activation of monitor systems from the tunnel’s fire detection system without manual intervention.

Zone Length

50–100 m

Each zone is the section of tunnel protected by one RCFM monitor. Shorter zones (50 m) for HGV tunnels; longer zones (80–100 m) for passenger vehicle tunnels with sufficient monitor throw range.

Monitor Position

Ceiling or wall mount

Mounted at the zone boundary or mid-zone depending on throw range. Ceiling mounting maximises coverage geometry; wall mounting allows maintenance access. Monitor-to-floor distance typically 4–6 m in road tunnels.

Water Supply

Dedicated fire main

Each zone has an independently controlled isolation valve. Only the activated zone valve opens — adjacent zones remain pressurised and ready. Ring main sized for simultaneous operation of the worst-case zone demand plus one adjacent zone.

Detection per Zone

Linear heat + CCTV

Linear heat detection (LHD) cable along the tunnel ceiling triggers zone-specific alarms. CCTV with video fire detection confirms fire position and allows operator visual verification before or during automatic activation.

Fire Detection Layer — Linear Heat and Video

Linear heat detection (LHD) cable installed along the tunnel ceiling provides continuous temperature monitoring at every point. When temperature at any point exceeds the alarm threshold (typically 90–110°C for road tunnels), the LHD system identifies the specific zone where the alarm originates and signals the tunnel management system (TMS). Video fire detection (VFD) cameras with smoke and flame detection algorithms provide visual confirmation. The zone identification from LHD is the trigger for the automatic monitor activation sequence.

Standard: NFPA 72 for fire alarm system design · EN 54-22 for LHD cable in European projects

RCFM Monitor — Electric Remote Control with IP65 Rating

The RCFM electric remote control monitor is the active suppression component. In a tunnel installation, the monitor receives the zone activation signal from the TMS, opens the zone isolation valve, aims to the programmed oscillation sector for that zone, and begins discharge — all without any human action. The monitor must be rated IP65 or higher for tunnel environments where exhaust fumes, humidity and occasional water spray create aggressive conditions. The motor drives must be sealed against dust and moisture ingress over a service life measured in decades.

For tunnels carrying hazardous materials (tanker routes): confirm whether the electrical motor and enclosure require ATEX Zone 1 or Zone 2 classification certification

Zone Isolation Valves — Independent Zone Control

Each protection zone has a dedicated electrically actuated isolation valve on the fire main branch supply to that zone’s monitor. The valve opens when the zone activates and closes when the zone is reset. This zone isolation ensures that only the fire-affected zone discharges — adjacent zones remain pressurised and ready for immediate activation if the fire spreads. Zone valves also allow individual zone maintenance (valve closed, monitor isolated) while the remainder of the tunnel system remains active.

Valve type: motorised butterfly or ball valve with position feedback to TMS · Fail-open design optional for critical tunnels

Tunnel Management System (TMS) Integration — The Control Layer

The TMS is the central control platform for all tunnel systems — traffic management, ventilation, lighting and fire suppression. The TMS receives the fire detection alarm from the LHD/VFD system, executes the pre-programmed fire response sequence (traffic stop, ventilation mode change, monitor zone activation, emergency broadcast), and monitors the status of all fire suppression components. The RCFM controller communicates with the TMS via a hardwired digital I/O interface or Modbus/BACnet protocol depending on the system architecture.

Operator at the tunnel control room can override or manually direct the RCFM from the TMS workstation at any time during or after automatic activation

LHD First Alarm — Zone Identified

Linear heat detection triggers in Zone N. TMS registers the alarm, identifies the zone, activates CCTV display at the control room for operator visual confirmation, and simultaneously begins the pre-programmed fire response timer. Traffic signals are set to stop incoming traffic. Emergency public address announcement activates for the affected tunnel section.

Confirmation Delay Expires — Automatic Monitor Activation

If the operator has not cancelled the alarm within the confirmation delay period (typically 15–30 seconds, project-specific), the TMS automatically signals the Zone N RCFM controller to activate. The zone isolation valve opens. The RCFM motor drives aim the monitor to the pre-programmed oscillation starting position and begin the oscillation sweep across Zone N. The monitor supply valve opens and discharge begins.

Adjacent Zone Pre-Pressurisation

The TMS pre-pressurises the isolation valves for Zone N-1 and Zone N+1 (adjacent zones on either side of the fire zone). This allows immediate activation of adjacent zones without the valve opening delay if the LHD system detects fire spread beyond Zone N. The ring main fire pump maintains full system pressure throughout.

Operator Override — Available at All Times

From the moment of first alarm, the tunnel control room operator can: cancel the activation before the confirmation delay expires; override the oscillation mode to fixed-aim at a specific position; activate adjacent zones manually; shut down the active zone; or re-aim the monitor to a specific angle. Manual override capability must be available and cannot be disabled by the automatic sequence per NFPA 502.

Why can’t a fixed water deluge system (like a sprinkler system) be used for tunnel fire suppression instead of monitors?

Fixed deluge nozzle systems (similar in principle to sprinkler deluge) have been used in some tunnels — particularly in Japan and Australia — and can be effective for controlling fire spread. However, deluge systems apply water across the entire zone area, flooding the tunnel with water and creating significant drainage challenges. They also activate the full zone area regardless of which part of the zone is involved. Automatic fire monitors provide directed attack — water goes specifically to the fire vehicle, not uniformly across the entire zone. This reduces total water consumption, minimises traffic disruption to unaffected lanes, reduces drainage system requirements, and allows the operator to adjust aim during the event. The two approaches have different cost profiles and are appropriate for different tunnel types and project risk profiles — both are accepted under NFPA 502.

How many RCFM monitors are required per tunnel zone?

The number of monitors per zone is determined by the design fire flow rate and the throw range coverage requirement. For a two-lane road tunnel (approximately 10 m wide) with a 50 m zone and an HGV design fire requiring 60–80 L/s total, a single monitor at the zone boundary or mid-zone with sufficient throw range (≥70 m) may cover the entire zone. For longer zones (80–100 m), or where the fire zone width requires more than one monitor’s throw range can cover, two monitors at different positions within the zone are specified. Always verify coverage by plotting the monitor’s range circle on the zone plan and confirming full zone coverage including the far corners of each traffic lane. The flow rate and range calculation guide provides the method for this calculation.

Does activating the tunnel monitor system affect ventilation operation?

Yes — and the interaction between monitor activation and tunnel ventilation operation is one of the most critical aspects of tunnel fire suppression system design. Water discharge from the monitor creates a significant volume of steam, which changes the aerodynamic and thermal properties of the tunnel airflow. NFPA 502 and most national tunnel fire safety standards require that the tunnel ventilation system is coordinated with the suppression system. Typically: when the monitor activates, the longitudinal ventilation velocity is reduced to a defined “critical velocity” level (the minimum velocity that prevents smoke back-layering upwind of the fire) — not zero, but not full extraction mode either. The specific ventilation response must be defined during the project fire safety engineering assessment and programmed into the TMS fire response matrix.

What is the required water supply duration for a tunnel fire monitor system?

NFPA 502 and most national standards require the fire water supply to be sufficient for continuous monitor operation for a minimum period that allows emergency responders to arrive, assess the situation and either take over manual firefighting or complete evacuation of all persons from the tunnel. This is typically defined as 60–120 minutes of sustained operation at full design flow rate. The fire water tank volume (or connection to a reliable municipal supply) and the fire pump sizing must both be verified to meet this duration requirement at the full design flow rate of the activated zone plus one adjacent zone.

Can automatic fire monitors be specified for rail tunnels as well as road tunnels?

Yes — automatic fire monitors are increasingly specified for rail and metro tunnels, particularly at station areas and in tunnel sections where trains carry hazardous materials. The design principles are the same as road tunnels: zone-based RCFM monitors linked to automatic detection, oscillating sector scan, and TMS integration. The key differences are: rail tunnel cross-sections are typically narrower than road tunnels (affecting sector width parameters); train length may exceed the zone length, requiring coordinated activation of multiple zones for a single train fire; and the detection system design must account for the high airflow velocities in piston-effect ventilation systems common in metro tunnels. Consult the applicable national rail safety standard for the specific requirements — NFPA 502 covers road tunnels; rail-specific requirements are governed by national rail safety legislation.