UKRO Humberside Education Workshop 2017 NATURAL GAS POWERED VEHICLES Some LGV manufacturers (currently IVECO and SCANIA) are able to offer and Alternative Fueled vehicles that use Compresses Natural Gas (CNG) and Liquid Natural Gas (LNG) for operation in the UK. They are able to operate throughout the UK and their range can be up to a thousand miles. These gas systems carry their own risks and the following information should assist crews to respond to incidents safely. Natural gas is lighter than air, unlike petrol or diesel, in the unlikely event of a leak it disperses in the air instead of forming pools. Unlike other fossil fuels (i.e. petrol, diesel and LPG), natural gas consists predominantly of a molecule naturally found in the environment which is methane. The methane molecule is very stable, neither toxic nor volatile. In addition the carbon emissions resulting from combusting methane are relatively low as the molecule contains only a single carbon atom therefore making the exhaust emissions lower, compared to its closest rival LPG (Predominantly Propane) which has three. Natural gas is the same gas that is used in the home for cooking and heating. It is compressed to 200 bars to save storage space on board vehicles. In Britain the fuel composition is 96% methane. IDENTIFICATION There are three fuelling systems which use LNG/CNG and which may be found in vehicles today: Vehicles and cars that carry both petrol and natural gas either of which can be used at the flick of a switch. These are predominantly found in Europe but could be on UK roads. Engines for this method operate on the spark ignition cycle. Vehicles that carry both diesel fuel and natural gas. The engine operates on the compression ignition cycle with diesel being used to start the engine and provide the heat to ignite natural gas as it is gradually introduced to the engine in ratios that vary according to operating parameters. When conditions are at their optimal the fuel mixture consists of about 80% natural gas and 20% diesel.
Dedicated Natural Gas Vehicles which operate only on natural gas, either compressed (CNG) or liquefied (LNG) such as the latest IVECO and SCANIA commercial vehicles and use large modified spark ignition engines. There is still a small diesel tank but this is for the heating system for driver comfort only. CNG CYLINDERS CNG cylinders may be constructed from either steel, a composite of steel, aluminium wrapped with carbon fibre, or a composite of plastic and carbon fibre wrap. The cylinder sizes vary with the type of vehicle to which they are fitted but may be between 60 to 90 litre water capacities (wc). Vans normally carry more than one cylinder to give a capacity of 90 to 180 litres (wc) whilst lorries and buses usually carry a number of cylinders with a total capacity between 350 and 1,000 litres (wc). All CNG cylinders are secured to be crashworthy and to resist the huge forces of an impact, and would normally be sited in the vehicles luggage compartment, however it must be borne in mind that the cylinders may be located in different locations from one vehicle to another. Some lorries will have very large cylinders that are easily distinguishable, whilst others that use the smaller cylinders will have them bolted onto a vehicle s chassis often on either side in purpose built compartments. Pipework is manufactured from stainless steel and is only attached to the structural members of a vehicle. Each cylinder incorporates a manually or electrically operated isolation valve and is protected by a pressure relief device that is likely to include a temperature sensitive fusible plug that will allow all the contents to disperse unlike the vent on a LPG system that opens and closes according to the internal pressure. Crews must be aware that in the event of a fire the pressure of the gas may rise due to the cylinder being exposed to heat causing the plug to open releasing contents of the cylinder to the atmosphere; this escaping gas may ignite producing a flame several metres in length. Other safety devices fitted include a deceleration switch, which will stop the flow of gas and isolate the cylinder if it is fitted with an electrically operated cylinder valve if the vehicle suffers a substantial impact. A vehicle may also be fitted with an excess flow device which will prevent the excessive flow from the cylinder in the event of a ruptured pipe or if the regulator pressure relief device is venting. The flammable range for natural gas is 5 to 15. Examples of CNG cylinders
LNG TANKS LNG storage tanks are cryogenic containers that consist of two insulated layers separated by a vacuum (effectively a large flask) to enable the natural gas to be stored in its liquid state at a temperature of -160 o and at a pressure of 7 bar. The flask is similar in appearance to a conventional diesel tank and is usually secured to the chassis of the vehicle usually between the front and rear axles of the tractor unit. High pressure gas is drawn off from the flask from the void above the liquid and routed through a series of pressure reducers and eventually fed into the engine. Despite the insulating properties of the flask some boil off will convert the liquid to gas raising the pressure within the tank. Normal use of the vehicle will relieve this pressure however if the vehicle is not used the gas will be automatically vented to the atmosphere to keep the contents of the tank at a pressure between 7 and 16 bar.
Isolation valve Example of LNG flask Warning label Open valve cover Closed valve cover The cylinders should be marked stating whether they are Compressed Natural Gas (CNG) or Liquid Natural Gas (LNG) as some vehicles have a combination of both cylinders. Refueling of Natural Gas Powered Vehicles There are two ways to refuel natural gas powered vehicles, fast fill and slow fill. In either case connection to the vehicles tank is completely sealed which does not permit gas or any evaporative emissions to escape. Fast fill is as refueling with a liquid fuel and slow fill refuels a vehicle overnight (approximately six hours). In each case the supply cuts off safely when the vehicles tank(s) are full.
Incidents involving Natural Gas Powered Vehicles In the absence of information from the driver of the vehicle or markings about its fuel it may be difficult to identify if a vehicle is gas powered. Indicators that a vehicle is gas powered are: The filling point may be labelled natural gas however this may be indistinct in a fire situation or sited behind the filler flap. The vehicle may have two filling points indicating that it is dual fuelled. (Petrol /LPG) If it is safe to do so it may be possible to locate the cylinder occupying the luggage space. (Cars) Most lorries powered by natural gas carry cylinders (CNG) or flasks (LNG) are bolted to the vehicle chassis often both side s and clearly visible and valve groups will have ice around them when they are operating. CNG used as a vehicle fuel is odourised and a smell of gas in the vicinity of an incident could well indicate a leak of gas from a vehicle. LNG is not odourised. The gas engines run quieter than diesel and there is a smell of gas from the exhaust system. A possible smell of gas from a CNG system. Unlike CNG, LNG is not odourised and the resulting gas from LNG will not have the characteristic gas smell. The sound of gas escaping. A mist of LNG indicating the vicinity of a leak. A pool of rapidly evaporating LNG below the leak. Many safety devices are incorporated into the fuel system of a Natural Gas Powered Vehicle, however there is still a possibility that an accident involving one of these vehicles could result in a gas leak or fire. Upon arrival at the scene of an incident crews are likely to find one of the following situations: 1. The vehicle is not alight and a gas leak is not immediately present. 2. A serious gas leak is detected or suspected 3. The vehicle is alight. 1. The vehicle is not alight and a gas leak is not immediately present It may be difficult, particularly from a distance, to determine if a vehicle is leaking gas but if the vehicle is damaged it should be assumed that it is, and therefore is at risk from fire until it has been established otherwise. The likely course of action for the above scenario: Assess the condition and location of any casualties. Assess the risk to them and the surrounding area. Make contact with the driver if possible to establish the nature of the vehicles fuel, secondary fuel and whether the vehicles ignition has been turned off. (Some cylinder isolation valves will operate when the ignition is switched off). Evacuate the area immediately around the vehicle extending further downwind. Eliminate any potential sources of ignition.
Layout firefighting jets. If cutting is to be undertaken, take care not to sever gas pipes and to use cold cutting non electric equipment. Consider the presence of other types of fuel, if there are no obvious signs of a serious gas leak (or the spillage of other fuels), and if it is necessary and safe to do so, close the cylinder isolation valves. A further safety precaution that can be undertaken in the absence of a gas/air mixture is the disconnection of the vehicle battery. 2. A serious gas leak is detected or suspected If there is a serious gas leak it must be assumed that the resulting gas cloud could ignite. The safe system of work will need to be re-assessed, the risk to firefighters is greatly increased and only if the benefit of continuing with the task remains greater than the risk it entails should the vehicle be approached. The following procedure should apply when dealing with gas leaks from vehicles: It is likely, in the event of a serious gas leak from a Natural Gas Powered Vehicle, that the only justification there can be to work in the immediate vicinity of the vehicle will be the preservation of life. BA should be worn and most of the actions listed previously should be implemented. Water sprays may help to disperse the gas clouds and only cold cutting non electric equipment should be used in order to release a casualty. Where life is not threatened, allow the CNG/LNG to disperse to atmosphere while, if necessary, protecting the surrounding area. When sufficient time has elapsed for the gas to escape, approach the vehicle employing all precautions previously listed. Consider the use of PPV. Do not attempt to ignite escaping gas. Ensure ventilation if the vehicle is indoors. A vehicle with a known or suspected leak should not be moved under its own power, i.e. if it has to be moved it must be towed or pushed. Use only intrinsically safe lighting and radio. 3. The vehicle is alight A fire in a Natural Gas Powered Vehicle may not be the result of a gas leak. It could follow from a fault in the secondary fuel system or it may have resulted from the usual causes of fire in vehicles. Whatever the cause, any major fire in a Natural Gas Powered Vehicle could result in the gas cylinder/s being weakened by the heat before the pressure release device/s have actuated and a risk of explosion exists. The procedures to follow are: Set up initial 200m Hazard Zone. Consider evacuation Assess the condition and location of any casualties. Use jet/sprays from a safe distance to cool the cylinders. This may be difficult as they are often shrouded by trim and bodywork. Do not extinguish the burning gas unless it directly threatens life. A flame from an open pipe carrying CNG may be several metres long.
Protect the surrounding risk and particularly, in the case of large vehicles, any part of the vehicle not effected by fire. IF IT IS SAFE TO DO SO, turn off the gas cylinders. This action will not prevent the pressure release device from actuating and releasing CNG. The flame from a pressure release device vent pipe will be several metres in length and should not be extinguished. Ensure full protective clothing and BA is worn Consider the possible involvement of a secondary fuel A thermal imaging camera may be able to assist in providing an indication of the relative temperature of the fuel cylinders.