Myth 5: CNG vehicles are not safe

In an interview with Down To Earth, Sheila Dixit, chief minister of Delhi, said, “even new (CNG) buses are not able to withstand the heat…I hope they will survive the heat this summer” (Down To Earth, April 30, 2001).

In another interview with Hindustan Times, Sheila Dikshit said, “No (safety) norms (for CNG kits) have been notified. The CNG vehicles are on the road without this clearance — we are playing with the lives of people, especially children. And I fear to think of how the CNG buses will perform in the middle of the summers. They are known to overheat…”

One self-styled expert has even remarked on TV, “Ten kg of CNG is like 10 kg of RDX”.

A cylinder blast is just what the anti-CNG lobby needs to prove that Delhi is heading towards a major disaster once the entire public transport converts to CNG (The Indian Express, April 7, 2001).


Fact

CNG, unlike LPG, is a gas that is lighter than air, it quickly dissipates into the environment and is unlikely to acquire enough concentration in the air to explode. Moreover, CNG has a higher flash point (the temperature at which the fuel is likely to explode on its own) of 540oC than petrol which has a flash point of 232-282oC

In the event of a vehicle collision, CNG fuel tanks are much stronger and safer than either diesel or gasoline fuel tanks, says the US Department of Energy.

The biggest safety problem in India is likely to be the use of spurious cylinders, especially when unauthorised agents for cars, taxis or autos carry out conversions from petrol to CNG. But the problem can be dealt with if adequate efforts are made. The Mumbai transport department has done this successfully.

it is not surprising that several people wonder whether CNG cylinders will explode when Delhi summer temperatures touch 45o Celsius. People have a right to be worried about safety (see box: There is no chance of the cylinder blowing up even if a bus catches fire).

But let us see how this works. When temperatures rise, gases expand. If kept in an enclosed space, pressure builds up. Companies manufacturing the cylinders should be able to say what pressure a CNG cylinder can take. If there are doubts, the cylinders can be tested by heating them in a laboratory. If found deficient — not just in normal summer temperatures but also in extreme situations like a bus catching fire — appropriate safety specifications can be set.

A petrol or a diesel tank can also explode — try throwing a burning match into one of them — but they rarely do. This is only because there are safety specifications. The government can easily take appropriate steps and keep people informed. But neither the state government of Delhi nor the Central government have cared to do anything.

In principle, CNG is quite safe. CNG, unlike LPG, is a gas that is lighter than air, quickly dissipates into the environment and is unlikely to acquire enough concentration in the air to explode. Moreover, CNG has a higher flash point (the temperature at which the fuel is likely to explode on its own) of 540oC than petrol which has a flash point of 232-282oC.34

CNG cylinders are put through severe abuse tests before the statutory authorities give approvals. They are tested to withstand pressure of up to 340 bars as against the working pressure of 220 bars. The Nagpur-based Chief Controller of Explosives (CCOE) using standards set by the Bureau of Indian Standards (BIS) certifies these cylinders35. Thus, the chances of them exploding are next to impossible.

Nobody has cared to find out that even Cairo, a hot desert city, is going in for CNG vehicles. If there is no fear of CNG tanks bursting there, why is this an issue in Delhi?
Let us not forget that the big future for transport will be fuel cells powered by hydrogen, the ultimate non-polluting fuel, but which is an even more inflammable gas with a flash point of 259oC.

Myths about the safety of CNG have been spread across the world. A statement from the US DOE says, “The technology for making CNG tanks is well known and mature. In the event of a vehicle collision, CNG fuel tanks are much stronger and safer than either diesel or gasoline fuel tanks. The few instances of CNG tank failures were studied carefully, and the problems, mostly involving support strap failure or tank abrasion during normal operation, have been remedied.”36

“CNG buses have some different safety concerns than diesel fuel buses, but overall, there is no evidence that CNG buses pose any greater risk of fire or explosion than diesel buses. Natural gas buses have on-board gas detectors and other safety equipment specially designed to ensure safe operation,” points out the DOE statement.

The biggest problem in India is likely to be the use of spurious cylinders, especially when unauthorised agents for cars, taxis or autos do conversion. For buses, conversion is being undertaken only by agencies which have been certified by the government, and therefore, the use of spurious cylinders is less likely. But even the problem of conversion in the case of cars, taxis and autos can be dealt with if adequate efforts are made as the Mumbai transport department has done (see box: Dealing with safety in Mumbai).

Ironically, despite the concern over safety, the regulatory agencies never cared to evaluate the safety regulations in force for CNG vehicles. CSE was concerned that if there were doubts about safety then it needed to be investigated and proper enforcement regulations and systems needed to be put in place to deal with the matter. In the absence of the official action in this regard, CSE decided to take it upon itself to get this evaluation done. So it invited three international experts, Christopher Weaver, President, Engine, Fuel, and Emissions Enginering, Inc., USA, Lennart Erlandsson of Motor Testing Centre, Sweden, and Frank Dursbeck formerly with TUV Rheinland Sicherheit Und Umweltschutz GMBH, Germany with wide experience in CNG technology to come and evaluate all currently available CNG technology in India. Their report (henceforth referred to as the CSE experts panel report on CNG) has provided valuable policy guidelines (Box: Safety matters: Issues raised by the CSE panel of experts.

    “There is no chance of the cylinder blowing up even if a bus catches fire”
A R Gulati, Director, Transport Engineering, Bureau of Indian     Standards, New Delhi, speaks with the Right to Clean Air Campaign team.

Who manufactures CNG cylinders in India and how are they certified?
There are three companies which manufacture CNG cylinders in India – Everest, Faber and Bharat Pumps and Compressors. These cylinders are manufactured in a special way to ensure that they can withstand high pressures. They are similar to oxygen cylinders which have been in use for a long time in India. Rules and regulations for this were laid down a long time ago and are called Static and Mobile Pressure Vessels Rules (SMPV Rules), which are followed by the Chief Controller of Explosives based in Nagpur.

The cylinders are manufactured according to India’s Pressure Vessels Code. This has been formulated taking into account the British Pressure Vessels Code as well as the US Pressure Vessels Code. This code has various parameters. Engineering parameters include size and dimensions, strength and so on. It also prescribes special parameters such as ‘relieving’. When a cylinder is being manufactured it experiences what is called stress and the metal becomes brittle. To get rid of this stress, ‘relieving’ is done. Several technical parameters are prescribed.

These cylinders are made in a special way. For the manufacture of normal cylinders, a metal sheet is moulded and welded but in case of CNG and other gases which are kept under pressure, a solid metal block, called a slug, is pierced from within to avoid any cracks. The chance of such a cylinder bursting is very rare.

Can the CNG cylinders withstand the heat of Delhi summer?

A CNG engine, similar to a petrol engine, generates a lot more heat to produce the same amount of power as compared to a diesel engine. That is why there is a chance that the area around the engine and near the driver may get heated up. But there is no safety risk from this.

What happens to a CNG cylinder or a kit when a bus catches fire?

I can assure you that there is no chance of the cylinder blowing up even if a bus catches fire. Yes, there will be dire consequences for the bus and the passengers but a certified cylinder will not burst.

Is it true that cylinders can withstand 340 bars pressure and the ignition temperature of CNG is 540 degree Celsius, as reported in the newspapers?
I am not sure of the exact pressure that a cylinder can withstand but it is at least 1.5 times the pressure under which CNG is stored, which is 200 bars. The flashpoint of CNG is 540oC. This is the temperature when CNG explodes on its own. The flashpoint of petrol and diesel is much lower than CNG.

Is there a danger in CNG vehicles in keeping the valve remains?

It is like keeping the regulator of your LPG cooking cylinder open. The valve is supposed to close on its own when not in use. If it is not functioning properly and gas continues to leak then it could be a problem. A CNG kit involves the actual conversion kit, pipes, valve and the whole system. Proper regulations for the valve are there in the draft document but they have yet to be notified.

What is the role of the Chief Controller of Explosives (CCOE) in the entire procedure? Does every cylinder have to go to the CCOE for certification?

A cylinder manufacturer first has to send the drawings and designs of the cylinder to the CCOE. After these are approved, the CCOE checks whether the proponent’s manufacturing facility is adequate or not. The qualification of the factory staff is also taken into account. Another important criteria is to make sure whether the manufacturer can consistently maintain the quality. Tests are carried out within the facility of the manufacturer where a prototype is examined. But even after this an inspecting authority is appointed to check whether the prescribed regulations are being followed by the manufacturer or not. Some of these inspecting authorities are the Director General of Quality Assurance (Defence), Lloyds Registering and Inspection Services, Engineers India Limited and Bureau of Indian Standards.

What is the role of the Automotive Research Association of India (ARAI) and other emissions testing agencies in the certification process and how is it different from that of the CCOE?
ARAI and other testing agencies come into the picture only when a new vehicle is fitted with a CNG kit, not when an old vehicle is fitted with a kit (in case of petrol vehicles). Balraj Bhanot is part of the committee that is formulating rules for kits.

Is there any way of keeping a check if the actual retrofitting of CNG kits is being done properly?
It is essential that qualified people and not roadside mechanics fit the kits. But what is happening today is that kit importers send their people to get trained in whichever place they are importing the kit from. These trained people then come back to India and impart their knowledge to others who then do the job. There is no system of testing and certifying kits in India. The rules and regulations for this are in the draft stage and are now being circulated. Today, the only criteria that the kit has to meet is to get a certificate from the country where it is manufactured. When a CNG kit importer gets a kit from abroad, the only thing that is examined is the certificate that importer gets from the country of manufacture. The kit, which comprises the valve, pipes and so on, is not tested. This is tested when a new vehicle is fitted with a kit or when a diesel bus is converted to a CNG bus by ARAI and other testing agencies. But there is no agency which checks whether a kit fitted to an old private car has been done properly. For this the Central Motor Vehicles Rules need to be amended.

What kind of measures should be implemented to check the use of spurious cylinders in CNG vehicles?
The Central Motor Vehicles Rules need to be amended to make an agency responsible for monitoring the installation of kits. This has to be amended by the standing technical committee formed under Ministry of Surface Transport (MOST). The members of the committee are Bureau of Indian Standards, Automotive Research Association of India (ARAI), Society of Indian Automobile Manufacturers and Vehicle Research and Development Establishment (Ahmednagar). The Indian Institute of Petroleum is not part of this committee.

Dealing with safety in Mumbai

A staff member of the Centre for Science and Environment who visited Mumbai in mid-April 2001 found that the government moved fast in Mumbai to deal with the problem of uncertified cylinders. When two blasts occurred (one in Ghatkopar and another in Chembur within one week of each other in March 2001) no one talked of CNG being an unviable option. The day the blast took place, the transport department immediately drew up a plan to check the use of spurious cylinders. In Mumbai, the responsibility is being put on Mahanagar Gas Ltd (MGL) for both supply and safety. The transport commissioner first made MGL responsible for issuing stickers after checking that the right cylinders (seamless and manufactured by either Faber India Ltd, Everest Canto, and Bharat Pump and Compressors — the three certified companies) were used and so was the kit and its fitting.

Initially, this drive was started at one or two dispensation stations and was extended to all 22 stations in the city. The inspectors included MGL engineers, NGOs (mainly volunteers and senior citizens), and members of the taxi drivers union. MGL conducted workshops for the inspectors so that they would know exactly what to look for.

So, within two days of the blast in Chembur, the entire checking system was functional. The transport commissioner set a deadline of March 31, 2001 by when he wanted all CNG vehicles to get stickers showing that they were using genuine parts after which they would be denied CNG at the dispensing stations. But another problem came up — the rain was washing the stickers away. The CNG committee, which has been constituted by the High Court to oversee the implementation of the orders, asked that the stickers be converted to metal tags which should be screwed on to the kit inside the bonnet. The stickers are now being gradually replaced with metal tags and a deadline of September 30, 2001 has been set. These will be done at CNG  stations from where the vehicle had got the sticker.

The government found that duplicate cylinders were being manufactured from scrap metal in one particular area in Mumbai. Scrap is available at Rs 4 per kg. These cylinders can be bought for anything between Rs 1,000 to Rs 3,000 while the original costs around Rs 10,000 upwards depending on its capacity. Some taxi drivers even say that pipes (used for water supply) were taken, the ends welded and used as cylinders. With this kind of gross mismanagement, it is surprising that only two blasts have taken place. Once the checks started, one or two offenders did come to light but managed to escape. The registration numbers of their cars have been circulated to all stations and the police are on the lookout.

The Transport Commissioner’s office has caught a couple of people manufacturing spurious CNG cylinders and a first information report (FIR) was lodged against them. They were put behind bars but they are now enlarged on bail. However, the blasts have really scared some of the petrol pump owners as they think that if something is not done soon, then their lives are at risk. In the meanwhile, some taxi operators have threatened the dealers that they have to be given CNG even if they do not have authorised kits.

Unfortunately, as a result of this the waiting time at CNG stations has become even longer. So now there are two lines — one for CNG dispensation and another for checking. Although the taxi drivers’ union has been raising a hue and cry about this, the authorities have not relented. They say that a taxi gets filled with gas only once a day so even if that means that the taxi has to queue up for a couple of hours,it is worth as this will eventually save lives.

Safety matters: Issues raised by the CSE panel of experts

In May, 2001, Centre for Science and Environment invited three international experts with wide experience in CNG technology, — Christopher Weaver, President, Engine, Fuel, and Emissions Engineering, Inc., USA, Lennart Erlandsson of Motor Testing Centre, Sweden, and Frank Dursbeck formerly with TUV Rheinland Sicherheit Und Umweltschutz GMBH, Germany, to evaluate the current emissions and safety regulations and CNG technology in India. These experts have pointed out the further scope of improvement in these areas to address the safety concerns.

Inspection of CNG vehicles

No provisions have been made for the inspection of in-use buses after conversion to CNG. In order to guarantee the compliance of the converted bus with the specifications of the type approved vehicle, it is important to inspect each and every bus before it is allowed on road. This inspection can be seen as equivalent to the foreseen conformity of production (COP) inspections for OEM CNG buses. This kind of system is already in place in many countries.

Each and every converted bus must undergo an inspection of the engine and high-pressure fuel storage system before being allowed on road. This inspection programme should subsequently be made annual for all operating CNG vehicles to check the emissions and safety compliance.

There should be a periodic inspection of CNG vehicles particularly those converted from diesel to CNG. The periodic inspection system in India consists of a road-worthiness inspection and a control of concentration of carbon monoxide in exhaust gas (maximum 3 per cent by volume at idle conditions). Going by experience in other countries, this is not sufficient to guarantee a correct functioning of the emission control system of CNG buses equipped with catalytic converters and closed loop mixture control. in a German Demonstration Project (BMU Demonstrationsvorhaben Emissionsarme gasbetriebene Nutzfahrzeuge) the following periodic inspection procedures for CNG vehicles have been very effective:
     

Visual check of components relevant to emission, including the exhaust emission system,
Measurements of carbon monoxide, hydrocarbons, carbon dioxide and oxygen levels with the engine idling,   Closed loop control check, and   Determination of nitrogen oxides and carbon monoxide levels under full engine load (as specified in rule 115,sub-rule 2 of the Central Motor Vehicle Rules) on a simple chassis dynamometer (which costs less than US $20.000).

This kind of inspection system should be introduced immediately as already a large number of CNG buses are operating for more than one year in Delhi. The inspection frequency for CNG buses should be set to one year, and combined with the annual road-worthiness check. Furthermore, all new and converted buses should undergo the same procedure before coming into operation in order to establish the reference values for the NOx standard and to verify that the closed-loop air-fuel ratio control is functioning properly.

As standards to be fulfilled at idle the panel of experts recommended the following:

For carbon monoxide: 0.5 per cent by volume at idle and 0.3 per cent by volume at high idle (1,700 ± 150 rpm for buses and HDT, 2,650 ± 150 rpm for light-duty vehicles and light-duty trucks).

For oxides of nitrogen: type-specific standards should be defined based on reference values derived from the initial exhaust concentration inspection.

Conversion workshops should be authorised
According to the Union ministry of road transport and highways (MRTH) notification, conversion kit installation on in-use vehicles can only be carried out by workshops authorised by the kit manufacturer/kit supplier. But requirement for these workshops, either legal or technical, have not been defined. This again is a reason for the recommendation made earlier to inspect each and every vehicle after conversion. MRTH must notify norms for the conversion workshops.

Other engine modifications desired

The experts panel noticed some flaws in the engines and engine designs of CNG buses as well. More detailed rules and guidelines for certification are required to deal with these.

In the production of the chassis, room for improvement lies in areas such as, material of the high-pressure piping, fixing of pipes to the chassis, tightening of the couplings, venting of the pressure relief valve and inspection of gas pipes. The experts felt that it should be avoided to mix brass fittings with pipes made of steel. Under moist conditions this combination could cause electro-galvanic corrosion. To avoid potential future problems with corrosion, they recommend the use of stainless steel fittings and tubing for high-pressure gas components.

Gas pipes should be mounted in such a way that movement and vibrations in the chassis are not transferred to the gas pipes, thereby causing a risk that the pipe could be broken or damaged by scraping after some time of use. It is common to use rubber wall tube insulators when bridging parts of the chassis and to attach the pipes to the chassis by the use of rubber pads. In addition, when vibrations cannot be avoided there should be enough room and length of the pipe to allow minor movements.

Experts have observed that leakage test is carried out after installation of the gas piping. This is necessary to identify whether there is leakage in the system. The leakage test is carried out by the use of soap-water brushed on each connection. Experts detected leakage in some places. To reduce the chance of leakage, it would be useful to use Teflon sealing tape in threaded fittings. Furthermore, it would be wiser to use compression fittings, where possible, or fittings with a tapered thread instead of cylindrical thread.

Each gas cylinder has a pressure relief valve to vent the gas if the cylinder is exposed to high temperatures or high internal pressure. As of now, the venting of the valve is not directed, thereby releasing the gas close to the cylinder. Since the cylinders are installed beneath the body of the bus, there is a risk that the vented gas will reach an area close to people or, in unlucky cases, may enter the passenger compartment. One solution would be to direct the venting of the pressure relief valve via a hose or piping to the roof of the bus. This would allow the gas to dissipate harmlessly upward, with little chance of contacting persons or ignition sources.

When a CNG vehicle has been in use for some time gas pipes should be visually inspected. However, gas pipes used in some case are covered with a protecting layer of plastic or rubber. This will make it very difficult to visually inspect the pipes. If stainless-steel tubing is used instead of ordinary steel, then it will not be necessary to cover the tubes to protect them from corrosion, and this will facilitate visual inspections.

Nozzles and safety

There are problems with the refuelling of vehicles with New Zealand Standard (NZS) nozzles mandated by the February 9, 2000 notification. Filling is slowed down by the frequent O-ring failures that these nozzles experience. Such failures occurred quite frequently at the refuelling stations, and they occur on average about every 20 fillings. This failure not only interrupts fuelling and requires replacement of the O-ring, it also creates a fire hazard due to the release of a significant amount of high-pressure gas.

Standardising all vehicle-refuelling receptacles on the NGV-1 standard would reduce fuelling time requirements and queues, and make possible more efficient use of existing compression capacity. It would also help to open other international markets to Indian CNG vehicles,as this fitting is by far the most common internationally.