Delhi's slap-dash CNG mandate poses fire, explosion dangers; 'tip of iceberg' found in report

Diesel Fuel News, Dec 9, 2002 by Jack Peckham

India's Supreme Court order that ultimately led to a mad rush to convert Delhi's diesel buses and taxis to compressed natural gas (CNG) and ban any clean-diesel option this year has led to more than a dozen bus fires (buses completely destroyed) and represents "only the tip of a much larger iceberg of large, sudden releases of gas during bus operations," according to a report for the environmental group that pushed the CNG mandate.

The "Safety of CNG Buses in Delhi" report (see: www.cseindia.org/htlm/cmp/apc_ndex.htm) by Swedish/U.S. CNG expert team (Lennart Erlandsson, MTC-Sweden, and Chris Weaver, Engine, Fuel & Emissions Engineering-U.S.) explains that "while a great majority of these [gas] releases do not result in a fire, any such release has the potential to do so."

While a serious fleet-wide safety investigation is warranted, "at present, root-cause investigations of sudden gas releases are not being done unless such releases result in fires," the study authors found.

Part of the problem could be traced to mis-specified "burst disk" pressure-relief devices (PRDs) for CNG tanks.

Some vehicle operators have replaced "burst disks" that often fail with stronger disks, in order to allow operators to put more gas in CNG tanks and thus extend the hours of operation between CNG tank refills. Delhi vehicle operators wait in queues for up to eight hours to refuel their CNG vehicles, with adjacent highways jammed and delaying all other traffic (as Diesel Fuel News experienced first-hand in a visit to Delhi this fall).

Most CNG vehicle operators refuel at night (following the high-passenger-load daytime business hours) and because that, high-cost CNG refueling infrastructure sits empty during the day, but is overwhelmed at night.

Problem: Switching burst-disks to enable CNG tank overfilling "could lead to explosion of the CNG cylinders if the burst disk does not burst when needed," the report points out.

What's more, the fleet problems are likely to get worse, not better.

"The existing fleet of CNG buses are primarily new vehicles near the beginning of their economic lives. As these vehicles age, it can be expected that they will develop additional safety problems, including problems due to leaks, corrosion, cyclic fatigue [from frequent refueling], accidental damage and incorrect or improper repairs... Because of the costs involved, many bus owners are likely to seek to avoid testing or replacing their CNG cylinders."

To overcome these growing safety problems, the report recommends creation of a new Safety Office bureaucracy to oversee these thousands of vehicles. So far, however, safety inspections on CNG vehicles are vastly inferior to what should be required, the report found.

What's more, nobody's checking for excess nitrogen oxides (NOx) and carbon monoxide (CO) emissions, a chronic problem with CNG technology due to oxygen sensor and engine tuning problems. These can lead to far higher NOx and CO emissions than the diesel buses they replace. Fully 40% of the Delhi CNG buses tested exceed 1% CO emissions limits -- a test that has since been scrapped, the report found.

While the Supreme Court and "green" group, Center for Science & Environment (CSE), cited fears of diesel fuel adulteration to justify a CNG monopoly for Delhi's buses and taxis (rather than allow clean-diesel competition), the recent "Mashelkar Committee Report" for India's auto-fuel policy pointed out that just as many or more problems can be found with the court's CNG monopoly scheme (see Diesel Fuel News 10/28/02, pl).

What's worse, exploding CNG buses could kill scores of people in crowded Delhi, unlike relatively safe, explosion-free clean-diesel buses.