ONE APPROACH OF AVOIDING FLAME FLASH BACK IS PROVIDING LIQUID SEALS IN THE FLARE SYSTEM THAT KEEP THE FLAME FRONT FROM PROPAGATING BACK INTO THE PLANT PIPING.

                      SIMILARLY, LIQUID SEALS ARE OFTEN INCLUDED AT THE BASE OF AN ELEVATED STACK TO HELP MAINTAIN A POSITIVE PRESSURE IN THE DOWN STREAM FLARE HEADER, TO ENSURE THAT ANY LEAKS IN THE FLARE HEADER WILL BE DISCHARGED INTO THE ATMOSPHERE ( RATHER THAN BACK INTO THE PLANT ) AND TO PREVENT AIR LEAKAGE INTO THE HEADER.  AIR LEAKAGES INTO THE FLARE HEADER CAN BE EXTREMELY DANGEROUS ( AS IT FORMS EXPLOSIVE MIXTURE WITH FLAMMABLE GASES/VAPORS ).  IF A LIQUID SEAL IS NOT USED AT THE BASE OF THE STACK, THE FLARE STACK SHOULD BE PURGED CONTINUOUSLY WITH AN OXYGEN FREE GAS, SUCH AS NITROGEN.

                       MECHANICAL SEALS LOCATED AT OR BELOW THE FLARE TIP CAN ALSO BE USED TO PREVENT FLASH BACK IN FLARE SYSTEMS.  THESE SEALS SIGNIFICANTLY REDUCE THE AMOUNT OF CONTINUOUS PURGE GAS REQUIRED TO PREVENT AIR INFILTRATION INTO THE FLARE STACK.  MOST MOLECULAR SEALS ARE PURGED AT A RATE OF 0.5 ft/Sec. TO KEEP THE FLAME OUT OF THE FLARE TIP.  VELOCITY SEALS ( WITH A SINGLE OR MULTIPLE BAFFLES ) REDUCE THE PURGE GAS VELOCITY THROUGH THE FLARE TIP TO 0.02 - 0.04 ft/Sec.