At present several thousands of CNG refuelling stations and millions of natural gas vehicles (NGVs) are operating all over the world. The great majority are working satisfactorily day in day out with a consistent operating and safety record. While most are constructed to comply with relevant standards, it should be remembered that standards are put in place as minimum requirements and that there is almost always more that can be done to improve the safety and operation of vehicles and refuelling infrastructure. ‘Best practice’ manufacturers and service providers should always be on the lookout for improvements.

What contributes to a well performing CNG installation? On the face of it improvements may appear to be difficult to find, given the advances already made in the quality and specifications of products and services, and the safety measures - over and above the CNG standards - demanded by the approval process of many regulatory authorities:

•    The number and capabilities of equipment and service providers have increased enormously over the years, steadily accumulating experience and product improvements.
•    The ongoing development of the standards, equipment technical and safety-related specifications have improved progressively, together with customers’ awareness of the need, and demand, to verify them.
•    In many countries, installations are required to be supported by studies such as site-specific quantitative risk analyses (QRA).

Factors improving the safety and operation of CNG facilities

The in-service safety of CNG installations, including CNG vehicles, depends equally on the quality of all project elements: installation design, equipment selection, installation method and operating procedures. As the operating life span of installations is considerably longer than all other project activities, operating procedures are of critical importance in the overall safety of the project.

While it is essential to adhere to standards and regulations, they may not cover some safety scenarios  in detail. In all cases , CNG projects will benefit strongly from:

•    Better customer knowledge to enable the customers to work together with the vendors to provide good solutions.
•    Good quality project specifications to reduce or eliminate potential safety issues. An example of this is the elimination of the practice of removing and retesting composite on-board CNG cylinders at periodic recertification time, as allowed by the new CNG cylinder standard. The extensive handling required by the previous cylinder standards was once the source of opportunities to inflict unnecessary damage to the composite which sowed the seeds of in-service failure.
•    Avoidance of excessive specifications to avoid unnecessarily costly installations. Conversely, avoidance of inadequate specifications helps to achieve performance adequacy and operational improvements.
•    Assurance of the fitness for service of equipment to produce improved safety outcome. For example, to avoid fatigue failure, correct gas cylinder designs should be used for refuelling stations with frequent and deep storage pressure excursions. Another example is the correct installation of gas storage systems, and appropriate fire protection provision, on CNG transport trucks and trailers to ensure safety in the event of vehicle fire.
•    Doing more than just complying with the minimum safety requirements of the standards to prevent costly safety incidents. For example, some years ago, some composite cylinders were mounted under the floor of CNG vehicles without mechanical guards against road debris. Even though the installation has been, and remains, approved (based on the earlier standards), safety improvements can – and should - be made by fitting mechanical guards.
•    Better knowledge of the safety performance of specific equipment items to enable installation to maintain better safety than just complying with the standards. For example, refuelling station standards specify safety requirements such as separation distances and hazardous area limits based on historical and statistical data of the class of equipment used. However, knowledgeable installation designers using newly developed equipment without an established safety record, or existing equipment with a lower than average performance, can achieve equivalent safety by modifying the distances accordingly.
•    Better knowledge of the operational and safety characteristics of CNG equipment to enable a check of the quality and correctness of specialised safety analyses, with the attendant improvement in costs and safety.
•    Operating procedures which are produced with expert input will include feasible safety scenarios and specify practical measures to address such risks. This is a considerable improvement upon procedures which are produced by generalists to be “in accordance with standards”, since modern standards are not prescriptive, that is, they do not give practical, installation-specific details.

Benefiting from better use of technical and safety knowledge

Given the high value of CNG projects, the primary objectives of achieving economic and safe installations and operations should be established right at the conception of the projects.

When best practice is applied to a project, significant economic advantages can be identified and realised, together with the all-important prevention of potential human and property losses from safety incidents. The cost of using the best practice approach will be more than offset several times over by the benefits it produces.

It is prudent to use expert input to achieve best practice outcomes in all stages beginning with project specifications, through installation compliance to the preparation of operating and maintenance procedures. While manufacturers and  and suppliers will always have experts on hand who can demonstrate compliance and performance, an independent expert can act as an advocate for a client, ensuring that the work done does in fact provide the best outcome for the client.  During the operating life of the installation, the same expertise can also guide modifications or improvements to the operating procedures in the light of new experience accumulated from the operation itself. As always, cost is a consideration but the cost of not calling on available expertise almost inevitably exceeds any avoided costs.

Dr Ly operates as an NGV industry consultant providing independent safety audits, incident investigation and safety training. He can be contacted at This e-mail address is being protected from spambots. You need JavaScript enabled to view it . This e-mail address is being protected from spambots. You need JavaScript enabled to view it