Project Complex fires – impacts of container failure

15/07/2019

• Challenge
• Methods
• Objectives
• Partners

The CoFI-ABV project examines and assesses the impact of accident-related critical failure of containers for alternative fuels in vehicles (CNG, LPG, LNG, hydrogen). Focus points include complex fire and explosion scenarios.

BAM carries out tests on its Technical Safety Test Site (including large-scale tests) within the framework of the CoFi-ABV project. Established site measurement technology is tested in various scenarios and further developed for specific applications. The tests are also the basis for a statistical data base that can be varyingly applied, including for probabilistic failure prognoses.

The results of the CoFi-ABV project will be incorporated in action-aids for fire fighters and rescuers. The data from experimental tests will form a solid basis for probabilistic failure prognoses.

The CoFi-ABV project is funded by BAM and does not involve a third party. There are several participating Divisions. In this project, BAM also works closely with the German Statutory Accident Insurance (DGUV), the HFUK and the Berlin Fire Brigade.

Complex fires – impacts of container failure (CoFi-ABV)

The acceptance of alternative fuels, in the form of liquid or compressed gases, is increasing because these gases are now regarded as clean. Alternative fuels include CNG (Compressed Natural Gas), LPG (Liquefied Petroleum Gas), LNG (Liquefied Natural Gas) or hydrogen. In contrast to petrol or diesel tanks, tanks for alternative fuels must be designed as pressure vessels and be equipped with a safety device such as a pressure relief valve. Nevertheless, the tank can be damaged in the event of accidents, which can lead to leakage or may impair the safety device and release gas, resulting in explosive fuel-air mixtures. Ignition of these mixtures then leads to a distinct pressure, temperature and heat propagation as well as to flying debris. The dangers of such scenarios are still difficult to assess for rescue workers today. So far, a superficial glance at a vehicle seldom indicates whether it operates on alternative fuel. Overall, there is very limited valid data. There is also no practical tool with which fire brigades can reliably measure the escaping gas from a safe distance.

In the CoFi-ABV project, BAM is investigating the consequences of accident-related failure of containers for alternative fuels. The results should provide, among other things, a basis for action-aids for fire fighters and other emergency personnel in the case of accidents or incidents. The results can also be adapted into safety distances for emergency personnel and passers-by.

Practical fire and explosion scenarios

The fire and explosion scenarios are designed practically, economically and reproducibly. To this end, the BAM engineers and technicians carried out preliminary tests using three different underfiring methods: wood fire, gas fire and a pool fire with petrol. They determined the effective heat input in the respective test specimen, i.e. in the gas cylinders or tanks. The pool fire proved to be best suited for the subsequent large-scale tests with storage containers for CNG, LPG and hydrogen. They investigated the impacts of the tank failure and the way in which tanks filled with different quantities of fuel behave in a fire. After the containers failed – exploded – they determined fragment number and mass, flight distances and scattering patterns.

An aim of this project is to validate and further develop measurement technology for specific applications. To this end, the engineers use mobile and robust measurement technology that is well suited for field applications. A mobile flight platform (UAV) is being tested for use in certain accident scenarios. This includes detecting methane from a safe distance for example. The flight control was programmed within the project. Data interfaces, the methane laser’s sensor integration, as well as the CT-based data evaluation have been established and are continuously being developed further.

A second important hazard scenario is continuous gas leakage from a damaged container. In this case, the gas can mix with ambient air to form a gas cloud that ignition can turn into a fireball. The test series systematically studies the so-called "untamped" gas cloud explosions.

Initial findings

The safety distances for possible container failures have been significantly increased on the basis of new findings regarding the flight range, heat radiation and pressure. BAM and the DGUV are preparing a leaflet for this purpose, providing a detailed description of the dangers involved in a propane bottle fire. More leaflets will follow regarding the previously examined fuel containers with LPG, CNG and hydrogen. A statistical database has been developed from the measurement data, which forms the basis for the preparation of a probabilistic failure prognosis. Test results on LPG and CNG tanks are currently being evaluated. The mobile flight platform is being further developed and the sensors are being miniaturised.