Flare System Start-Up Checklist: 15 Checks Before First Ignition

September 19, 2026
Safety

A flare is the last line of defence on a process plant, and first ignition is the moment it either starts working or starts arguing with you. Most failures at this stage are not exotic. They come down to purge gas that never reached a dead leg, a pilot orifice nobody cleaned, or a trip valve tested at the screen instead of in the field.

The checks below cover the pre-commissioning window: mechanical completion is signed, lines have been pressure tested, and someone is keen to send gas to the tip. Work through them in sequence. Later checks usually depend on earlier ones, and the flare should stay isolated and depressurised until they are done.

None of this replaces your site procedure, the vendor's instructions or the relevant standards — API 521 and API 537 remain useful starting references for flare design and operation — but it should stop the obvious things being missed.

1–2. Before anything is purged

Start with the paperwork and the field, in that order, and do not let the two drift apart.

Verify the documents and the revision. The cause and effect matrix, P&IDs, purge procedure, valve line-up sheets and the flare datasheet should all be at the correct revision and should match what is actually installed. If a drawing and the plant disagree, resolve it before you open a valve.
Walk the line-up valve by valve. Include the purge gas route, pilot gas and fuel gas headers, knockout drum drains, seal drains and every isolation point. Confirm that all temporary blinds, spades and test plugs are removed and logged — a blind left in a pilot gas line is one of the classic reasons a first ignition fails. Lock or car-seal anything that must not move.

3–5. Purging and inerting

Purging is where impatience costs the most time. It is also where the readings matter more than the schedule.

Confirm the purge medium is available and reliable. Whether you are using nitrogen or fuel gas, check supply pressure, dryness and any flow indication. For a fuel gas purge, confirm composition and make sure the source cannot be isolated without an alarm reaching the control room.
Purge in the order the procedure states, and sample where it matters. Take oxygen and combustible gas readings at high points, branch connections and dead legs, not just on the main header. Record them as the purge progresses. Dead legs take far longer than anyone expects, and instrument tappings are easy to forget.
Once purged, keep it purged. A continuous sweep holds the header slightly positive so air cannot creep in through the tip, drains or instrument connections, and it keeps the mixture in the stack outside the flammable range. Confirm the rate, the measurement method, and the alarm that warns if purge is lost.

6–9. Seals, arrestors and liquid removal

Molecular or fluidic seal. Check internal components, alignment and drains. The seal should be clean and free of debris, with drain holes clear. If the procedure allows a bypass for purging, confirm it is closed afterwards and recorded.
Flame arrestor. Element intact, clean and correctly oriented, with the housing free of rubbish and no blocked passages. If pressure drop can be measured, check it against the vendor's figure.
Liquid seal and knockout drum. Seal depth set as designed, level instruments proved, high-high level trip tested, boot drain and pump operation checked. Heat tracing or insulation should be on where liquid could freeze.
Header drains and low points. Drain everything, confirm traps and drain valves are clear, and look for sagging where support or expansion problems leave liquid sitting in the header.

10–12. Ignition systems

This is the part everyone wants to reach. Give it the same care as the rest.

Pilots and their gas supply. Check pressure at the tip, filters, regulators and orifices — clean the orifices even on a new system. Light each pilot and confirm a stable flame on its own detector. Cross-reading from the neighbouring pilot is an easy trap to fall into.
Flame detection and annunciation. Test each detector through to the panel and the control system, prove the pilot-out alarm, and check any auto re-ignition logic. The alarm needs to reach someone who can act on it, not just a screen in an empty room.
Igniter. For a flame front generator, check air and fuel supply, spark plug gap, transformer and cable. For a high-energy igniter, check continuity, insulation resistance and travel to the tip. For a manual system, confirm the correct cartridges and a safe firing position. Then check the ignition panel's UPS or battery backup and prove that remote start from the control room works.