Overview
ISO 19723-1:2018 - Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 1: Safety requirements - specifies minimum safety requirements for LNG on-board fuel systems fitted to motor vehicles defined in ISO 3833. The standard covers systems used in mono‑fuel, bi‑fuel and dual‑fuel applications that use LNG in accordance with the ISO 15403 series. It applies to the LNG system components up to and including the vaporizer and excludes downstream CNG components (covered by ISO 15501). The document also excludes matters relating to installer/converter skills and - as stated in the scope - is not applicable to original‑production and converted vehicles.
Key topics and technical requirements
- Scope of coverage: Components in the LNG system (tanks, valves, flexible fuel lines, fittings, vaporizer, etc.) and connecting parts fitted on motor vehicles.
- Design requirements:
- Components must withstand operational and environmental temperatures (LNG ≈ −162 °C at atmospheric pressure).
- Location, mounting and protection against impact, corrosion, road debris, heat and chemical splash.
- Minimize galvanic corrosion and ensure proper electrical conductivity and grounding to avoid electrostatic charge.
- Component-specific rules:
- Tanks and pressure systems designed per service pressure and ISO 12614 series.
- Pressure relief valves (PRV): primary PRV must vent via a pipe‑away to a high level; secondary PRV outlets must be protected and not share the same pipe‑away.
- Excess flow limiting devices: allowed inside or directly on the tank and may be integrated with LNG/CNG automatic valves.
- Automatic valves: must be normally closed when deactivated and only open when LNG operation is selected and the engine is cranking or running.
- Refuelling receptacle: must comply with ISO 12617, include a cap and nearby marking (fuel type and service pressure).
- Safety systems: venting system, gas‑tight housings or natural gas detectors for certain vehicle categories, isolation valves, check valves, and provisions up to the vaporizer.
- Documentation and marking: instructions for use and component marking requirements.
Practical applications - who uses this standard
- Vehicle manufacturers (OEMs) designing LNG‑powered vehicles (M and N categories per ISO 3833).
- Component and system suppliers (tanks, PRVs, receptacles, valves, vaporizers).
- System integrators and safety engineers for vehicle-level safety design and routing of LNG lines.
- Test laboratories and certification bodies conducting compliance and type‑approval testing.
- Fleet operators and specifiers seeking safe LNG vehicle procurement and maintenance guidance.
Related standards
ISO 19723-1:2018 is essential reading for anyone responsible for the safe design, manufacture or certification of on‑board LNG fuel systems for road vehicles.