In this sub-activity, field tests have been executed at a fire brigade training location where it is possible to bring an amount of 1300 kg LNG to an open pit of 6,25 m2 which has been provided with a perlite insulation layer at the bottom to create a stable rate of evaporation of the liquid, making it well suited to study its behavior in detail.
Based on this facility, a series of experiments have been designed to give answer to the following three questions:
a.For the purpose of creating a realistic training environment where the LNG is not expected to burn, could liquid nitrogen (LIN) be a safe replacement of real LNG?
b.What are the consequences for the fireman realizing that LNG is a cryogenic liquid?
c.What is needed to minimize the risk of ignition of a potentially explosive gas mixture?
Answers and most important other conclusions from the experiments are as follows:
1.To simulate visual aspects of evaporation LNG, LIN is a good alternative to LNG. It evaporates however much faster than LNG and therefore a test with foam coverage to stop the evaporation is not realistic;
2.Normal PPE for the fireman is not suitable for contact with the cold LNG, dedicated equipment is needed when a risk exists of direct exposure to LNG;
3.A water mist screen based on very fine droplets is capable of controlling the heat release of an LNG pool fire effectively and even allows to some extend repressive action although typically one would prefer to let the fire continue until all the LNG is vaporized, avoiding the development of a new, potentially explosive gas cloud again;
4.Trying to control the gas release from a burning LNG pool with regular water accelerates the vaporization only and enhances the fire;
5.A dedicated hydrocarbon camera is able to detect methane in air at levels as low as 40-50 ppm which is about 0,1 % of LEL. A visible cloud (ice crystals in the air) typically has a CH4 concentration which is far above ignition concentrations (>15%) but as soon as these ice crystals disappear, gas concentration drops rapidly to levels below the ignition window. This limits the area where a cloud could ignite.
The field tests all have been captured on video and pictures to be used for training purposes. Lessons learned from this work will be transferred to a range of Protocols and will be distributed to all relevant fire brigade desks.