All over the world, new alternative fuels are emerging to replace fossil fuels such as gasoline and diesel. The overall benefits are great but with new fuels and technical solutions, new risks emerge.
The first responders face new situations that they are not familiar with and have to make decisions that they are not trained for. The lack of education and experience may have consequences on the society due to which kind of decision that was taken.
On today’s biogas-powered buses, the gas tanks are equipped with temperature fuses to ensure that the vessels do not explode due to the increased pressure resulting from heating of the vessels. The temperature fuses activate when the temperature passes about 110 degrees Celsius. This means that all of the gas is released at a high pressure out to the surroundings. In most of the known cases where CNG buses has caught fire the temperature fuses has worked in a correct way and the gas has been ignited when leaving the vessel causing a massive jet flame. However, Lionel Perrette and Helmut K. Wiedemann describe in their article Safe Storage of Natural Gas on Urban Buses: Case Early Investigation and Learnings three different fire incidents where the fire has led to explosions of vessels. The reason for these explosions was not the failure of the temperature fuse. The vessels exploded when they were heated on a single spot that did not affect the temperature fuse. One question that has to be raised is if the only problem with biogas-powered busses is fire in the vehicle with risk of explosions or massive jet flames? What happens for example if the bus is involved in traffic incidents where the gas system in some way has been damage and a leakage has occurred? For the last years in Sweden, several traffic incidents has happened where the gas system on the bus has been damaged and the rescue leader has been afraid that leakage has occurred. Then a decision needs to be taken, but it is not always obvious what decision would be the correct to take.
Biogas-powered bus traffic incident in Gothenburg
In June 2013 a traffic incident occurred in the central parts of Gothenburg. Involved in the incident were one personal vehicle and the CNG (Compressed Natural Gas) bus shown in Figure 2. As shown in Figure 2 the personal vehicle had only touched the bus in the front. The damage on the bus could only be seen as small buckles and discoloration under the front window. What differed this incident from an “ordinary” traffic incident was that the bus had its CNG fuelling nozzle and a manometer placed in the front, and the manometer
had been damaged in the collision, causing a small leakage of natural gas. The risk with leaking natural gas is that the gas is easy to ignite and have a flammable range from 4 to 16 vol %, causing a large explosive area if leakage occurs.
The rescue leader from Greater Gothenburg Fire & Rescue Services gave initial orders to close all the nozzles on each gas cylinder to stop the flow of gas. After one hour the gas flow had not stopped. The rescue leader was thinking about following three choices:
- Keep the closures (150 m) and wait until the cylinders are empty. This would take about 4 days. High risks with the central location in Gothenburg, all surrounding buildings and the infrastructure.
- Empty the cylinders by removing each nozzle. Also high risks with the central location in Gothenburg, all surrounding buildings and the infrastructure.
- Towing away the bus to a safer area and then empty the cylinders. High risk to ignite the leaking gas with sparks from the tow truck.
Due to high risks with all these three choices the decision was to disconnect as much electrical device in the bus as possible and drive the bus with the ongoing leakage in the front out of the city to a safe place and then empty all cylinders. This decision had effects on the society by having a closure of 150 m in the city for a few hours, and the traffic was stopped for a short time when the bus was driven out of the city. The incident commander was thinking in terms of following events due to the nature of each decision alternative. Other decisions could have had huge consequences on both the infrastructure and the general public. Due to the complexity in the society and in technical systems (in this case biogas-powered bus), it is more and more important to think in terms of escalating consequences when the incident commander selects what kind of decision he/she will make. This kind of escalating consequences can be called cascading effects, i.e. one incident starts and a chain of subsequent events follows. Depending on what kind of decision the incident commander makes, the chain of subsequent events can take different turns. One simple example of explaining this is a fire at a car repair company. In the building gas cylinders are stored for welding equipment. The rescue leader takes the decision to evacuate the area and keep the enclosure for 24 hours according to recommendations where gas cylinders are involved in a fire. Next to the car repair company is the highway and railway; these are also closed for 24 hours. The stop in the railway and highway system has huge consequences on the society.
Modern socio-technical systems are increasingly characterised by high degrees of interdependencies. Whereas these interdependencies generally make systems more efficient under normal operations, they contribute to cascading effects in times of crises. Therefore, challenges for emergency preparedness and response are growing significantly – challenges which are more and more relevant to both natural and manmade emergencies and are reinforced by the risks for cascading effects in complex emergency management environments. In particular complex environments which lack adequate resilience to certain initiators will be prone to cascading effects. An escalating incident in such an environment can lead to severe cascading effects and quickly become extremely difficult for emergency services to handle. The incident can ultimately have enormous consequences with respect to life, property and the environment and for both infrastructure and the general public. These consequences can in many situations have both direct and indirect effects, not only in the immediate surrounding geographical area but also across very large areas, potentially extending across borders.
The EU-project CascEff
SP Fire Research is coordinating the EU-project CascEff and performs the work together with 10 other partners from Europe. In CascEff four of the main objectives are:
- Better understanding of the cascading effect in crisis situations.
- Develop an Incident Evolution Tool for predicting past, present and future crisis evolution leading to cascading effects.
- Identification of human activities in the crisis.
- Improved incident management for present and future threats.
CascEff will improve our understanding of cascading effects in crisis situations through the identification of initiators, dependencies and key decision points. These will be developed in the methodological framework of an Incident Evolution Tool which will enable improved decision support, contributing to the reduction of collateral damages and other unfortunate consequences associated with large crises. Use of the Incident Evolution Tool will be validated through its implementation into different incident management and training platforms representing different end users in the project (e.g. NoKeos, iCrisis, RIB, WIS and XVR). A roadmap for similar implementation in other incident management and training platforms throughout Europe will be defined to allow broad acceptance of the Incident Evolution Tool.
For more information, go to www.casceff.eu