Explosion Avoidance
Safety relief valves and vent lines The potential of a hazardous explosive atmosphere around those points has to be evaluated and a zone classification around those areas may be required depending on location , construction and operating procedures . It is common practice and recommended by DIN 4754 to lead such “ emission points ” to a safe place at the outside of buildings by welded piping . As a consequence , the classification of the rest of the heat transfer plant is not influenced .
Sample valves In a properly designed heat transfer plant , special oil sample drafting devices should be installed . The representative oil sample is cooled down to temperatures below 50 ° C before drafted .
Tanks For tanks that might contain organic heat transfer fluids above their flash point , a zone classification for the interior of the tank may be required . This can be avoided when the tank is covered by an inert gas like nitrogen .
Emergency shutdown For the emergency shutdown of all electrical equipment , an emergency switch has to be installed in the power supply line . This switch has to be installed in a safe area ; usually outside the heat transfer systems room . Equipment which has to be operational after emergency shut-down , like escape route lighting , shall be safeguarded against explosion hazards .
Conclusion Finally , it can be concluded that if all the above mentioned standards and design criteria are considered and state-of-the-art equipment is used , it is good practice to operate heat transfer fluid systems without any classification of explosion areas deriving from the presence of the organic heat transfer fluid itself . We hope that these statements contribute to your efforts to find a technically feasible solution and get a clear and objective picture on the basis of technical arguments .
About the author
Dr . -Ing . Andreas Glück studied general mechanical engineering at the University of Stuttgart from 1983 to 1989 and completed his doctorate at DLR in 1996 on the subject of high-temperature thermal energy storage systems . He then worked in plant engineering in the field of process heat supply / temperature control with a focus on plants with organic heat carriers , so-called " thermal oils ". He is co-founder and managing partner of heat11 GmbH & Co . KG in Bielefeld , a specialist in designing and manufacturing of process heat plants in the temperature range from -100 ° C to + 480 ° C .