Unmanned Stations, Populated Surroundings, No Margin for a Missed Leak

A city gas distribution network is unusual among industrial assets: it is almost entirely unmanned, and it sits inside the community it serves. A pressure reduction station can be metres from housing, a school or a busy road. That combination — no one on site, everyone nearby — sets the standard the detection has to meet.

ZE-Tronics supplies and maintains gas detection, flame detection and safety control systems for pressure reduction and metering stations, district regulators, odorisation plant and distribution control rooms, with the engineering, installation and accredited calibration all provided locally.

Pressure reduction and metering stations

The hazard at a PRMS is accumulation. Gas escaping inside a regulator kiosk has very little volume to disperse into, so a leak that would be trivial in an open process area reaches a hazardous concentration quickly. Detection has to be sited for where methane actually goes — upward, and into the roof space of the enclosure — rather than at convenient mounting height.

• Infrared point detection at high level in regulator kiosks and metering halls
• Open-path infrared across larger halls, compressor buildings and station perimeters
• Ventilation interlocks and forced extraction on first alarm
• Slam-shut, vent and remote isolation interfacing on confirmed alarm
• Ex-rated beacons and sounders for anyone on site during a maintenance visit

Below-grade chambers and valve pits

Valve pits and below-grade chambers are the part of a distribution network where fixed detection and enclosed space entry procedures meet. Gas collects in them, they are entered for maintenance, and the person entering is often alone. Fixed detection covers the accumulation risk between visits; portable detection and a proper entry procedure cover the person. Both need to be calibrated and both need records, and the two regimes should be designed together rather than by different departments.

Odorisation plant

Odorant handling deserves its own engineering. Mercaptan is detectable by smell at extraordinarily low concentrations, which is the point of it, but that also means a small spill produces a very large public response. The storage, injection and transfer equipment has its own hazards, its own containment requirements and its own detection thresholds, and it should be treated as a distinct area rather than folded into the general station scheme.

Detection technology for methane

Infrared point detection is the usual choice. It is stable over long unattended periods, it cannot be poisoned, and it fails safe: if the optics are obscured, the detector reports a fault rather than reading zero. Catalytic sensing still has a place where the gas mix includes hydrogen, because infrared sensors physically cannot detect it — a consideration that is becoming less theoretical as hydrogen blending is trialled in distribution networks.

Open-path infrared is used where the space is large enough that point detection would need an impractical number of sensors: a metering hall, a compressor building, or a line across a station perimeter. It complements point detection rather than replacing it — a beam confirms that gas has crossed a plane, a point detector confirms the concentration at a specific location.

Telemetry that tells the control room something useful

An unmanned station is only as safe as the information it sends. A bare alarm contact tells the control room that something happened; it does not tell them whether a detector has genuinely seen gas or has simply failed. Modern detectors provide digital diagnostics, live readings, fault states and calibration status, and passing that through to SCADA changes what the control room can decide without dispatching anyone.

• Per-detector identity, reading and diagnostic state reported to SCADA
• Calibration due status visible in the control room, not only in a spreadsheet
• Confirmed voting before automatic isolation, with clear manual override
• Event history retained for incident review and regulatory reporting

Functional safety, not just equipment

Where detection initiates an automatic action — closing a slam-shut valve, starting extraction, isolating a section of network — that action is a safety function, and it carries a required integrity. IEC 61511 and IEC 61508 provide the framework for specifying and verifying it. In practice this means being explicit about what the system must do, how reliably, and how that reliability will be demonstrated in proof testing, rather than assuming a certified device produces a certified function.

Retrofit is the normal case

Most distribution network work is retrofit into stations that are already in service. The limits are usually physical and operational rather than technical: how much room the existing enclosure has, where the existing cable routes run, and how long the network can tolerate a station being isolated. We plan installations around those constraints, sequence work so isolations are short and coordinated, and document every impairment while it exists.

Calibration that reflects the fleet

Distribution networks operate large populations of identical detectors across many sites, and that is an advantage: once the calibration record exists, intervals can be justified from real drift behaviour rather than assumed from a manufacturer’s default. Our AZS ISO/IEC 17025:2020 accredited laboratory calibrates fixed and portable gas detection with traceable results, and our electronics repair bench restores detectors and controllers in country so spares keep circulating.

Explore our calibration and maintenance services, or ask us to review detection across your network.