NGV Cylinders Built to Gas Transport Standards Increase Safety, Reduce Liability
By John Coursen
Product Line Manager, Alternative Fuel Cylinders
Worthington Industries (Special to Fleets & Fuels)
Like many in the natural gas vehicles industry, Worthington Industries is concerned about the increasing number of compressed natural gas cylinder rupture incidents. Such incidents raise obvious safety concerns, and as well, NGV fleet owners and manufacturers are exposed to significant liability risk, which might eventually threaten the growth and adoption of NGVs.
The field history of composite cylinders is teaching that current CNG cylinder standards are not adequately protecting the industry and the public. In particular, CNG cylinders are governed by much lower safety standards as compared to what has been traditionally required for composite cylinders used on watercraft, aircraft, railcars and in bulk gas transport (often called gas transport cylinders in these other industries).
More specifically, National Highway Traffic Safety Administration (NHTSA) NGV cylinder regulation FMVSS 304 and NGV cylinder standard ANSI/CSA NGV2 allow a much lower design burst safety factor (2.25 times service pressure) than gas transport standards (at least 3.0 times service pressure).
‘Vulnerabilities Are Real’
Additionally, NGV cylinder standards do not require any demonstrated impact tolerance in the critical cylinder sidewall region where stresses are at a maximum. Consequently, cylinders designed according to current NGV standards can have a less durable structure that makes them more prone to rupture from impact events, extreme heat/fire, corrosion and other forms of degradation that can occur while in use.
The field history of composite cylinders teaches that these vulnerabilities are real and that gas transport standards are far more effective in protecting the public safety. Importantly, there has never been a reported rupture incident among the estimated 1.5 million carbon composite gas transport cylinders that have been placed in service by multiple cylinder manufacturers since carbon fiber first became commercially available in the early 1990s.
More Cylinders, Older Cylinders
In contrast, the NGV industry at first averaged slightly more than one NGV cylinder rupture event per year from 1993-2008. However, the frequency of rupture incidents has increased as the first generation of NGVs age and as the number of NGVs has increased. In 2014 there were two separate NGV cylinder rupture incidents in the U.S. (one due to an impact event and another due to fire). Two more NGV cylinders have ruptured so far in 2015 (due to fire in the same incident).
Worthington believes NGV fleet operators, vehicle manufacturers, NGV upfitters and cylinder manufacturers invite significant products liability risk if they choose to follow current NGV cylinder standards. There have already been multi-million dollar claims arising from NGV cylinder rupture incidents. More will likely result from the 2014 rupture incidents. Parties should, of course, consult with their own counsel, but compliance with industry standards is not an absolute defense in many jurisdictions. In fact, it may turn out to be a weak defense when one compares the historic safety record of NGV cylinders and gas transport cylinders.
NGV Passengers Deserve Aircraft-Level Protection
Worthington instead believes that NGV owners and passengers deserve the same safety protections as traditionally required for gas transport cylinders in aircraft, watercraft, and railcars, which is why it builds its cylinders to gas transport standards.
Fleet operators can also take a proactive stance concerning their NGVs by inquiring about their vehicles’ fuel cylinders prior to purchase – that includes their physical makeup and to what standard they have been built. Doing so is a smart step towards improved safety and reducing liability.
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Source: Worthington Industries with Fleets & Fuels follow-up