ISO 15501-1:2016

Overview

ISO 15501-1:2016 - Road vehicles - Compressed natural gas (CNG) fuel systems - Part 1: Safety requirements specifies minimum safety requirements for CNG on-board fuel systems used in road vehicles (as defined in ISO 3833). It applies to mono‑fuel, bi‑fuel and dual‑fuel vehicles, both original production and conversions, using compressed natural gas in accordance with ISO 15403. Installer competency and training are excluded. The document is based on a nominal service pressure of 20 MPa (200 bar).

Key topics and technical requirements

ISO 15501-1 sets out functional and safety design requirements for CNG fuel systems with emphasis on the following areas:

• System components and design

  • Requirement to comply with component standards such as ISO 11439 (cylinders) and ISO 15500 (CNG components).
  • Components must withstand environmental temperatures, mechanical damage, automotive fluids and UV exposure (for fibre‑reinforced cylinders).
  • Ensure electrical conductivity to avoid electrostatic charging (where applicable).

• Cylinder and valve arrangements

  • Mandatory automatic valve on every cylinder plus a manual isolating valve.
  • Pressure‑relief devices (PRDs) installed per cylinder and additional PRDs as required by ISO 11439.
  • Excess‑flow valves or functionally equivalent systems to limit abnormal gas flow.

• Refuelling connection

  • Receptacle must comply with ISO 14469, include a protective cap and permanent markings showing “CNG”, cylinder inspection date and service pressure.

• Pressure control and protection

  • Downstream components protected from regulator failure (pressure relief inside regulator or equivalent).
  • PRD configuration guidance: parallel or thermal relief devices recommended; series PRDs limited to type 1 steel cylinders.

• Installation, mounting and safety features

  • Cylinder mounting, heat protection (clearances or shields), venting, leakage control, minimization of ignition risk, and accessibility for inspection.
  • Automatic valves normally closed when deactivated; considerations for start‑stop systems noted.

Applications and who uses this standard

ISO 15501-1 is used by:

• Vehicle manufacturers (OEMs) designing factory CNG systems
• CNG system integrators and component suppliers (cylinders, regulators, PRDs, receptacles)
• Conversion companies producing aftermarket CNG conversions
• Test laboratories and homologation bodies for vehicle approval
• Fleet operators and safety engineers defining procurement, inspection and maintenance criteria

Practical uses include system design verification, safety audits, procurement specifications, homologation documentation and maintenance guidance.

Related standards

• ISO 11439 - High pressure cylinders for on‑board storage
• ISO 14469 - CNG refuelling connector
• ISO 15500 (all parts) - CNG fuel system components
• ISO 15501-2 - Test methods for CNG on‑board systems
• ISO 15403 - Natural gas fuel quality
• IEC 60079-10-1 - Explosive atmosphere classification
• ISO 3833, ISO 1176 - Vehicle definitions and terminology

Keywords: ISO 15501-1, CNG fuel systems, compressed natural gas, road vehicles, safety requirements, CNG on-board, PRD, refuelling receptacle, ISO 11439, ISO 15500.