" The heater coil shall be subjected to pressure test by competent person once at least in every 12 months. The test pressure shall not be less than twice the operation pressure."  

"Before starting the furnace it shall be effectively purged."

_{All heater shall be provided with the following safety devices:-}

_{(i) level control in the expansion tank;}

_{(ii) temperature control of thermic fluid;}

_{(iii) differential pressure switch on the out let line of the heater tubes; and}

_{(iv) temperature control devoice for the fuel oil supply to the burner.} 

_{All above devices shall have interlocking arrangement with burner so that in} 

_{case of any predetermined limits being crossed the supply of fuel and} 

_{air to burner shall automatically be cut-off.}