Closing the Safety Loop Secures NGV Fleet Investment

| Asia | Source: Dr. Hien Ly, CFS International Pty Ltd

Bangladesh trainees visit an authorised gas cylinder test station in Sydney, Australia.

For many fleet operators, the introduction of natural gas vehicles brings with it new safety considerations. Dr Hien Ly, an independent consultant in the natural gas vehicle arena, outlines some of these considerations, and the value of using qualified experts to fill important knowledge gaps.

“The sooner the safety program starts the more assured fleet safety will be.”

For some time now, the international natural gas vehicle industry has had in place active programs aimed at maintaining and improving CNG vehicle safety. Safety implementation is a necessary adjunct to vehicle acquisition and asset management policies for every fleet manager. It includes projects to produce technical standards and codes of practice, formal training courses for technical personnel, safety workshops at conferences and CNG cylinder safety workshops.

Despite these endeavours, CNG vehicle safety incidents continue. The author’s experience with CNG bus fleet safety audits and investigations – for both fleets which have had incidents and those that have not – has indicated that, to provide a high degree of assurance, safety programs should not only be focused on particular areas but encompass the wide range of a fleet’s CNG vehicles, facilities and activities.

What contributes to the safety of CNG vehicles?

The safety of CNG vehicles comes from careful adherence to standards and regulations, the use of quality components, good installation design and workmanship, safe operating and maintenance procedures, and staff and driver training.

Fleet owners and operators also need to consider the safety of the workshops which install and service the vehicles, and the parking or garaging facilities in which they are stored. The facilities need to be correctly designed and equipped for CNG to meet occupational health and safety requirements including routine operational safety, fire safety and emergency response procedures.

Safety of CNG vehicles

The primary principles for designing and installing safe CNG vehicles are quite well known. They include:

  • Assurance of the fitness for service of equipment. For example, on-board fuel cylinders have to comply with recognised standards, or approved by the regulatory authority in the jurisdiction of use. Importantly, they must be in an acceptable physical condition after installation.
  • Adequate protection of on-board gas systems (including the fuel cylinders) against in-service damage or deterioration, e.g. from road debris; engine exhaust heat; exposure to engine fluids, ultraviolet light and chemical cargoes (in the case of composite cylinders); and mechanical contact with the rest of the vehicle. Such damage has caused cylinder (both metal and composite) failures in service.
  • The incorporation of good fire protection features for the on-board gas storage system to minimise the possibility of vehicle fire and to prevent cylinder failure if vehicle fire does occur.
  • Better knowledge of the operational and safety characteristics of CNG equipment to facilitate safe on-board installation or location. An example is the venting of the system’s pressure relief valve(s) to the outside to eliminate vehicle fire risk or passenger safety risk in the event of PRV discharges.

While they may be easily understood in principle, vehicle fleets that do not meet these requirements have either had safety incidents or been grounded for repair or and rectification, with operational disruption and financial losses.

Safety of CNG vehicle facilities

As identified by IANGV’s 2006 study on the gaps in international standards and regulations for NGV, there are very few national standards for CNG vehicle workshops. Two countries with such standards are Australia and Singapore.

In principle, CNG vehicle workshops should include:

  • Adequate working space provisions
  • Effective ventilation for the operating environment
  • Gas detection, alarm and lockouts for facilities that house vehicle over long periods such as overnight.
  • Fire protection/fire fighting equipment and procedures
  • Warning system for CNG vehicles being serviced
  • Safe operating procedures in normal operation as well as “increased hazard” situations
  • Staff training
  • Emergency system and procedures
  • Emergency response training for staff and external emergency services.

Safe work procedures

CNG vehicle safety depends on not only safe equipment and installation but also vehicle operating and maintenance procedures. Issues that have been identified in this area include:

  • Procedures may have been produced “in accordance with standards and regulations” by persons without the necessary knowledge and experience with CNG safety. However, this may not be enough, as modern standards are not prescriptive; they specify the desired safe outcome, not the essential vehicle-specific details.

Vehicle operating and maintenance procedures need to be reviewed by persons with suitable CNG safety knowledge. Independent external experts may need to be used if such expertise does not exist in-house. The review should consider feasible safety scenarios and specify practical measures to address such risks.

  • The periodic inspection of the on-board CNG system should pay adequate attention to the effects of the operating environment, including the cylinder mountings on the cylinders in service. For in-situ inspections such as allowed by ISO 19078, where difficult-to-access areas may be overlooked by inexperienced inspectors, this entails not only looking for the cylinder damage/deterioration in the right places but also predicting possible unacceptable damage/deterioration before the next scheduled inspection.

This capability in turn requires the inspector to have good knowledge of cylinder mounting systems, not just the cylinder rejection criteria as provided by the standards or cylinder manufacturers’ guidelines.

  • Vehicle workshop operating procedures in the event of known or suspected gas leaks from vehicles; and correct procedures for fighting a CNG vehicle fire, whether it involves the on-board CNG system.
  • Correct understanding and implementation of the safe work procedures by operating and managerial personnel. This can be ensured by providing adequate and timely training on CNG safety.

A program to ensure the safety of CNG bus fleets

CNG vehicle fleets tend to acquire relatively large numbers of vehicles of the same design. This gives the fleet owner the opportunity to carry out safety assurance work at a relatively low per-vehicle cost, helping to maximise return on investment.

With CNG bus fleets, in particular, the combination of large numbers of similar vehicles, their high economic value, and the high economic and human costs of their safety incidents make such work both highly cost-effective and socially desirable.

The safety work program should include:

  • Technical tender specifications including the requirements of standards and regulations, and the safety principles outlined above.
  • Tender evaluation which includes the tenderers’ compliance with the vehicle safety specifications.
  • Compliance certification of the components (including the fuel cylinders) and the on-board CNG system installation prior to vehicle delivery.
  • Vehicle operating and maintenance procedures – including the inspection of on-board fuel cylinders – which are appropriate to the type of operating environment and the type of cylinder mounting system used.
  • Ensuring that the vehicle workshop(s) and parking facilities are suitably upgraded for CNG vehicles, using an accepted standard such as AS 2746 in Australia or TR 10 in Singapore.
  • Training of personnel on CNG safety issues.

When should the safety program start?

Obviously, safety would be best assured if the safety program is implemented at the vehicle acquisition stage, right through to vehicle disposal at the end of their service life. However, this may not be practical or possible where vehicles have been purchased and are already in active service. As a rule, the sooner the safety program starts the more assured fleet safety will be, so operators who have not had a program in place should give strong consideration to starting one as soon as possible, picking program elements that are appropriate to the stage of development of the fleet.

The above article was based on the author’s work with several large CNG vehicle fleets. CFS International Pty Ltd ( is an NGV industry consultancy providing safety audits of CNG vehicle fleets, vehicle workshops and refuelling stations, incident investigation and CNG safety training. Dr Ly can be contacted at

Opinions expressed in this item are those of the author. Publication by NGV Global does not imply endorsement or agreement.

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