TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The collecting unit is arranged relative to the water based safety valve such that gas, and/or foam are prevented from passing between the collecting unit and the liquid based safety valve. The collecting unit is arranged with respect to an inner wall of the gas collecting zone that gas and/or foam may pass between the inner wall and the highest point of the collecting unit. The collecting unit defines an upper and a lower surface and a thermal insulator is provided between the upper and the lower surface. The collecting unit is inclined relative to a horizontal direction to guide the collected gas cooling liquid towards the liquid based safety valve. The collecting unit is arranged such that the gas cooling liquid which is collected during use drips into the liquid based safety valve. The lowest point of the collecting unit is positioned directly above the inlet of the liquid based safety valve(s). During operation of the apparatus, a vertical line extends through the lowest point of the collecting unit and a liquid surface of the liquid based safety valve. The liquid based safety valve defines a liquid outlet, and the liquid outlet is arranged to allow excess liquid from the liquid based safety valve to exit the liquid based safety valve. The liquid based safety valve defines a first and a second liquid trap which are arranged in series. The liquid based safety valve defines a gas outlet which is arranged such that gas will escape the liquid based safety valve when the first liquid trap does not contain a predetermined amount of liquid. The liquid based safety valve is accessible from an outer surface of the apparatus. The liquid based safety valve is slidably arranged in the apparatus such that it is slidable between an inserted position in which it is positioned inside the apparatus in the gas collecting zone, and a removed position in which it is accessible outside the apparatus. The first and the second liquid traps define a first and a second liquid zone, respectively, in which liquid is provided during operation, and the first and the second liquid zones are fluidly connected such that when a by-pass valve is in an open state liquid may flow from the first liquid zone to the second liquid zone, while liquid is prevented from flowing from the first to the second liquid zone through the by-pass valve, when the by-pass valve is in a closed state. The nozzles are arranged such that when the gas cooling liquid is sprayed out through the nozzles, the gas cooling liquid is sprayed into a foam which during use of the apparatus and is generated by the organic material thus it ascends from the gas generating zone into the gas collecting zone in which it continues towards the biogas outlets, and the nozzles are adapted to spray an amount of the gas cooling liquid sufficient to prevent the foam from entering the biogas outlet. The nozzles are adapted to function as fire and/or explosion preventing unit.