ISO 19723-1:2025

Overview

ISO 19723-1:2025 - Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 1: Safety requirements defines the minimum safety requirements for on-board LNG fuel systems fitted to motor vehicles (ISO 3833 vehicle types). The standard covers assembly components (tanks, valves, flexible fuel lines, fittings, etc.) and connecting parts up to and including the vaporizer. It applies to mono‑fuel, bi‑fuel and dual‑fuel vehicles, both original‑production and converted vehicles, and references the ISO 15403 series for LNG quality.

Key topics and technical requirements

ISO 19723-1:2025 focuses on safety design and functional requirements for LNG on-board fuel systems. Major topics include:

• System design principles - Components must conform to ISO 12614/12617 series and be designed based on declared service pressure.
• Component requirements - Tanks, pressure relief valves (PRVs), check valves, fuel pumps, fittings and flexible lines are covered; materials and placement must resist environmental, chemical and mechanical damage.
• Refuelling interfaces - Receptacle location, mounting and minimum clearance requirements to ensure safe and accessible refuelling.
• Leakage control and venting - Requirements for venting systems, PRV ventilation lines and vent line closures to safely manage LNG boil‑off and relieve pressure.
• Mounting, heat protection & corrosion - Rules for tank mounting, protection from heat and road debris, and minimizing galvanic corrosion.
• Ignition risk mitigation - Measures for electrical conductivity, grounding and minimizing sources of gas ignition.
• Instrumentation and controls - Inclusion of electronic control unit (ECU) requirements for engine demand control and automatic valve cut‑off on pipe break or engine stall; gas temperature sensing requirements.
• Documentation - Instructions for use, marking and inspection access requirements.
• Scope limit - Standard applies only up to and including the vaporizer; downstream components are treated as CNG components (see ISO 15501 series).

Annex A provides technical solution examples; Annex B lists typical LNG on‑board system components.

Practical applications and users

ISO 19723-1:2025 is used to:

• Guide OEMs and vehicle system designers integrating LNG propulsion systems.
• Define compliance criteria for component manufacturers (tanks, valves, vaporizers, connectors).
• Support conversion companies and engineering teams responsible for converted LNG vehicles (design compliance; installer skills excluded).
• Inform safety engineers, certifying bodies and regulators evaluating on‑board LNG system safety and conformity.
• Complement test methods in ISO 19723-2 for verification.

Related standards

• ISO 12614 (LNG fuel system components)
• ISO 12617 (LNG refuelling connector)
• ISO 15403 (LNG fuel quality)
• ISO 15500 / ISO 15501 series (CNG components)
• ISO 12991 (LNG tanks)
• ISO 19723-2 (Test methods)
• ISO 20653 / IEC 60529 (IP protection)

Keywords: ISO 19723-1:2025, LNG fuel systems, road vehicles, safety requirements, LNG on‑board fuel system, vaporizer, pressure relief valve, ECU, venting system.