Industries
Tunnelling – Fixed Gas Detection Systems
Environmental Monitoring Systems designed to meet BS6164 and beyond.
BS 6164 is the British Standard Code of Practice for health and safety in tunnelling in the construction industry. It specifically mandates the use of environmental and gas monitoring systems to ensure a safe working environment within tunnels and shafts.
Key aspects of gas detection under BS 6164 include:
- Mandatory Monitoring: The standard requires continuous monitoring of toxic gases, flammable/potentially explosive gases, radioactive gases (if appropriate), and oxygen levels in tunnels and shafts.
- Specific Pollutants: The 2019 revision places significant emphasis on monitoring Diesel Particulate Matter (DPM), classifying diesel engine exhaust as a carcinogen. It recommends a limit value of 100 µg/m³ (15-minute time-weighted average, measured as elemental carbon).
- Monitoring Locations: Fixed environmental monitoring stations are typically required at intervals of 300m to 500m along the tunnel, at each working face, and inbye of each airlock.
- Monitoring Type: The standard advocates for continuous, real-time monitoring from fixed locations to effectively analyse and respond to changing atmospheric conditions and validate control measures. Portable monitoring equipment is used to supplement the fixed systems.
- Warning Systems: The monitoring equipment must provide both visual and audible alarms to warn of unsafe levels of gases or low oxygen content, and there must be a clear communication system to the surface.
- Action Levels: Work must stop and the area be evacuated if oxygen content falls below 19% or if gas concentrations exceed safe limits set out in BS 6164 or HSE guidance EH40.
Why gas detection matters
Unplanned gas releases cause injury, ill health, fires, explosions and production downtime. UK employers have legal duties under DSEAR (Dangerous Substances and Explosive Atmospheres) and COSHH to manage risks from hazardous gases.
An engineered gas detection system forms part of a layered defence: identify, detect, alarm, isolate and evacuate.
Applications:
- Fixed detection
- Portable monitoring
- Confined-space safety
- ATEX-certified equipment
Our approach
Survey, design, deliver, support
Site survey & hazard mapping
Identify fugitive emission points, process vents, confined spaces and likely release directions.
Specification & zoning
Select sensor types and certify equipment to match DSEAR/ATEX zones and COSHH requirements.
Installation & integration
Fixed detectors, control panels, BMS/SCADA integration and alarm management.
Commissioning & verification
Calibration, functional tests and documented acceptance tests.
Maintenance & training
Scheduled calibration, sensor replacement, alarms testing and operator training.
Types of sensors & when to use them
- Catalytic bead — Broad-range combustible gas detection; economical; suitable for many hydrocarbon gases but susceptible to poisoning.
- Infrared (NDIR) — Long life and selective for hydrocarbons/CO₂; ideal for confined-space and outdoor installations.
- Electrochemical — Best for toxic gases (H₂S, CO, NO₂); high sensitivity and low detection limits.
- Oxygen sensors — Monitor oxygen depletion or enrichment; critical for inerting operations or confined-space entry.
- PID (photoionisation) — Detects VOCs at very low ppm levels — useful for solvent handling and leak detection.
- Open-path / beam — Rapid detection across a sweep area for flammable vapours — reduces number of point sensors needed.
Sensor placement & coverage - practical guidance
- Place fixed sensors at likely release points and along probable gas flow paths (not just where easy to install).
- Mount hydrocarbon sensors low for heavier-than-air gases (e.g. propane/LPG) and higher for lighter-than-air (e.g. methane).
- Consider ventilation patterns, shelving, piping penetrations and process enclosures; model dispersion where necessary.
- Use open-path beams across doorways, flume lines or along pipe corridors to detect releases quickly over a distance.
- For confined-space entry, always use monitored, calibrated portable detectors and follow a written rescue plan.
Regulatory snapshot (UK)
DSEAR — requires risk-based controls for explosive atmospheres.
COSHH — requires monitoring and control of hazardous exposures where applicable.
ATEX/IECEx — equipment certification for hazardous zones.
Employers must assess, document and implement measures including gas detection where appropriate.
Quality & standards
Systems are designed to recognised standards and best practice: BS/EN guidance for gas detectors and control panels, site-specific acceptance tests and documented maintenance regimes.
Key services
- Hazard & zoning surveys
- Fixed & portable equipment supply
- Installation, BMS integration
- Calibration & maintenance contracts
- Training & emergency response drills
Maintenance, calibration & lifecycle
A gas detector is only useful if it works when you need it.
Implement a written maintenance plan covering periodic calibration (or bump tests), sensor replacement, alarm checks and record-keeping.
Maintain traceable calibration certificates and keep a log of alarm events and corrective actions.
Recommended checks:
- Bump test before use (portable) or weekly checks for fixed systems depending on risk.
- Full calibration at manufacturer-recommended intervals, or when readings drift.
- Battery and communications checks for wireless devices.
- Functional testing of alarm outputs, relays and integration with shutdown systems.
Typical system architecture
From field sensors to control and action: sensors → junction boxes → control panel / PLC / safety system → operator HMI & alarms → SCADA/BMS logging.
Modern systems offer data logging, remote telemetry and secure cloud-based dashboards for compliance reporting and trend analysis.
Example features:
- Multi-channel control panels with redundant relays
- Event logging and time-stamped alarm histories
- Remote telemetry (4–20mA, Modbus, BACnet, IoT gateways)
- Operator access levels and audit trails
FAQs
Do I always need fixed detectors?
Not always — you must perform a risk assessment. For continuous processes with significant gas inventory or explosion risk, fixed detectors are usually required.
How often should detectors be calibrated?
Follow manufacturer guidance and the site risk assessment — typical intervals are 3–12 months. Perform bump tests more frequently.
Can gas detectors be integrated with my SCADA System?
Yes — common protocols include Modbus, 4–20mA and BACnet. Ensure cybersecurity and fail-safe behaviour are considered in the design.
Contact & next steps
Ready to secure your factory with a compliant gas detection system?
We offer site surveys, bespoke system design and full lifecycle support. Tell us about your facility and hazards and we’ll propose a practical solution.
