Flame Detector Selection Guide: UV, IR, UV/IR (UVIR) and Multispectrum IR3 Explosion-Proof Flame Detectors for Oil and Gas, Offshore Platforms, Aircraft Hangars and Gas Turbine Enclosures

A fixed flame detector has to see the fire you care about, at the distance you need, without alarming on the welding, sunlight and hot machinery around it. This guide compares published data for UV, single-frequency IR, UV/IR and multispectrum IR (IR3) flame detectors from Det-Tronics, Spectrex, MSA and Honeywell, read on October 14, 2026, and shows which detector fits which job.

Quick answer: which flame detector fits your application?

For hydrocarbon fires in hazardous areas the usual fit is a multispectrum IR (IR3) detector with heated optics and a self-test; UV, UV/IR and hydrogen detectors cover the special cases.

• Offshore oil and gas platform: multispectrum IR with heated optics, a stainless steel housing and marine approval, such as the X3301 (DNV type approval TAA00000V2; USCG approval as part of the Eagle Quantum Premier System).
• SIL 2 hydrocarbon detector with HART and a Division 1 rating: the X3301 Safety-Certified version with HART, the SharpEye 40/40C-I, the FL5000 and the FS24X Plus each list SIL 2, HART and a Division 1 marking (strings in the table).
• Aircraft hangar: IR3 with hangar processing, such as X3301 Hangar Mode: FM lists a 2 x 2 feet Jet A fire at 300 ft (91.4 m) in 9 s at very high sensitivity (outdoors, with pre-burn).
• Gas turbine enclosure: X3301 turbine (T-Low) sensitivity, 50 ft (15.24 m) in under 4 s for a 1 x 1 foot n-heptane fire.
• Hydrogen fires: the X3302 (30-inch hydrogen plume at 125 ft) or the SharpEye 40/40C-M.
• Fast suppression (NFPA-33, under 0.5 second): high-speed X5200, X9800 or X2200 models.

What is the difference between UV, IR, UV/IR and multispectrum IR (IR3) flame detectors?

A UV flame detector senses ultraviolet radiation (185 to 245 nanometers on the Det-Tronics X2200), a single-frequency IR detector watches one infrared band (4 to 5 microns on the X9800) and judges its flicker, a UV/IR detector alarms only when both sensors see the flame at once, and a multispectrum IR detector compares several IR bands (three IR sensors on the X3301). Each trades speed, range and nuisance-alarm behavior differently, and each has fuels it cannot see.

• UV and UV/IR (UVIR): the X2200 is solar blind, and the X5200’s auxiliary relay can be set to UV-only alarm for non-carbonaceous fires.
• Multispectrum IR (IR3, triple IR): the Spectrex SharpEye 40/40C-I uses four IR bands between 4 μm and 5 μm, the Honeywell FS24X Plus three bands from 0.7 μm to 5.0 μm, and the MSA FL5000 covers 2 to 5 microns.

Which false alarm sources does each flame detector type reject, and which can still trip it?

UV detectors ignore sunlight but react to other UV sources, single-frequency IR detectors ignore steady heat but can react to hot objects that flicker, and UV/IR detectors need both signals at once. The X3301 and FL5000 manuals publish FM tests with sunlight, arc welding, lamps or heaters in view.

• UV and UV/IR: the X2200 may respond to arc flash, arc welding, grinding metal, lightning, high voltage corona and x-rays, and flickering IR plus welding UV at once will produce an X5200 alarm.
• Multispectrum IR: at very high sensitivity the X3301 gave no alarm in FM testing from sunlight, arc welding at 40 ft (12.2 m) or a 1500 w radiant heater at 3 ft (0.9 m), and with arc welding at 40 ft it still saw a 32-inch methane plume at 125 ft (38.1 m) in 6 s; gas welding still mandates system bypass.
• Manufacturer guidance: MSA recommends its FL5000 where arc welding, plasma cutting, lightning or intense direct sunlight are present, though its FL500 UV/IR is on average slightly faster.

How far can a flame detector see, and how fast does it respond?

A detection range only means something with the fuel, fire size, sensitivity and response time attached: the X3301 sees a 1 x 1 foot n-heptane pan fire at 265 ft (80.7 m) in an average 22 s outdoors at very high sensitivity, and the same table gives 100 ft (30.5 m) in 3 s. Gas fires are rated as a plume: 125 ft (38.1 m) in 5 s for a 32-inch methane plume on the X3301.

• Same fire, other technologies: Det-Tronics rates the same 1 x 1 foot n-heptane fire at 85 ft (25.9 m) for its UV, UV/IR and single-frequency IR detectors, in 3 s, 14 s and 15 s.
• Read the footnotes: outdoor tests, pre-burn times and EQP models (plus 2 seconds) change the comparison.
• Response time: it depends on sensitivity, distance, fuel and fire growth; typical figures are under 10 seconds for the X3301, 10 seconds for the FL5000, 5 seconds (10 seconds maximum, FM witnessed) for the FS24X Plus and under 5 seconds for the Spectrex 40/40C.
• High speed has a price: the X9800’s Quick Fire responds to an intense fire signal in less than 30 milliseconds (0.030 seconds), but Det-Tronics recommends UV standard signal processing (no arc rejection) for high-speed suppression systems only.

What does the cone of vision (field of view) on a flame detector datasheet tell you?

The cone of vision is the angle across which the detector still meets a stated share of its on-axis range, so check the percentage as well as the angle. The X3301 states 90° horizontal by 75° vertical at a minimum of 70% of the on-axis detection distance, while MSA defines FL5000 field of view at 50% of maximum range and Honeywell gives the FS24X Plus a 120° cone at 50% of on-axis range.

• Catalog versus tested cone: Spectrex catalogs the 40/40C-I at 100° by 95°, while its manual says the field of view per FM testing is 50 degrees.
• Aim and limit the view: Det-Tronics recommends the Q1201C laser aimer and offers the Q2033 with a 30°, 20° or 10° sight limiter; PE lists the laser aimer holder and the weather shield and FOV limiter.

What blinds a flame detector, and why do heated optics and automatic optical integrity testing matter more than a test lamp?

Smoke, absorbing vapors, oil, water and ice between fire and detector shorten its range, so it should check its own optics and keep them warm. The X3301 runs a calibrated automatic optical integrity (oi) test once per minute and signals a fault when less than half of the detection range remains; FM verified the fault at a loss of approximately 50% of range.

• UV-absorbing vapors: heavy concentrations of ammonia, benzene, hydrogen sulfide, toluene or xylene restrict UV detection; Det-Tronics states its multispectrum IR is less affected than UV by lube oil and smoke.
• IR-absorbing vapors: in the 4.2 to 4.7 micron band the exceptions are triple-bond compounds such as acetylene, nitriles, silane or isocyanates, and CO2 above normal levels.
• No test lamp: FM says the magnetic or manual oi test replaces the need of a traditional external test lamp, and the X5200, X9800 and X2200 need none either; PE also lists Det-Tronics test lamps for detectors without oi.
• Other self-tests: MSA’s COPM checks the FL5000 optics once every 2 minutes (an obstruction may take up to 4 minutes to report); Spectrex tests every 15 minutes.
• Heaters differ: the X3301 lens heater defaults to 35° Celsius; the FS24X Plus heater turns on at -25°C, and Honeywell notes that at -55°C warming the electronics can take up to 30 minutes, during which the current loop reports less than 1.5 mA.
• Proof testing: the X3301 oi proof test is yearly; MSA and Honeywell test with lamps at 10 to 35 feet (TL105) and 10-25 ft (TL-2055).

Which outputs should a flame detector give your fire and gas system: relays, 4-20 mA, HART, Modbus or LON?

Choose the output your panel can supervise: relays, a current loop with HART, Modbus, or a digital loop such as the Eagle Quantum Premier (EQP) LON. The X3301 has fire, fault and auxiliary relays rated 5 amperes at 30 Vdc, a 0-20 mA option with HART and RS-485 Modbus, or comes as an EQP model on the LON/SLC loop with no analog or relay outputs.

• Map the current levels: the X3301 signals 0 mA power fault, 2 mA oi fault, 3 mA high background IR fault, 4 mA normal and 20 mA fire alarm; Spectrex uses 2 mA for a BIT fault and 16 mA for a warning.
• Relays differ: Spectrex and Honeywell relays are rated 2 A; the FL5000 has separate instant and sustained alarm relays rated 8 A @ 24 VDC.
• Know what is not supervised: the X3301’s 0-20 mA loop is not monitored by its fault circuitry, RS-485 is not available on its HART models, and FL5000 Bluetooth communication disables the safety function while active.

Which approvals should a SIL 2 hydrocarbon flame detector carry: Class I Division 1, ATEX, IECEx, FM 3260 or EN 54-10?

Check the hazardous-location marking, fire performance approval and SIL scope separately, copying each from the current label or data sheet. For the X3301, FM lists “Explosion-proof for Class I, Div. 1, Groups B, C, and D (T4A)” and performance verified per FM 3260 (2018), and IECEx ULD 06.0017X marks the increased-safety model Ex db eb IIC T6…T5 Gb and the flameproof model Ex db IIC T6…T4 Gb.

• Gas groups differ: of the models compared here, only the FS24X Plus prints Group A for Division 1 (“cFMus: Class I, Div 1, Grps A,B,C,D”). Group A is part of the hazardous-location marking, not a fire test; for hydrogen fires check published hydrogen tests.
• Division 2 is not Division 1: Honeywell’s FSL100 is certified for ATEX Zone 2/22 and FM Class 1, 2, 3 Div. 2, typically looking into a Div 1 area from outside it.
• SIL scope: exida rates the X3301 and X3302 “SC 2 (SIL 2 Capable)”, and only the Safety-Certified version identified on the label is for low demand SIL 2 systems; Spectrex states suitability per IEC 61508 up to SIL 2 single-channel or SIL 3 redundant; ask for the SIL certificate.
• Certificates with the quote: the exida certificate posted on det-tronics.com is Revision 4.0 of March 15, 2022 and lists a surveillance audit due February 1, 2025; ask Det-Tronics or PE for the current revision and for current FM and marine certificates.

Which multispectrum IR flame detector fits an offshore oil and gas platform with good false alarm rejection?

An offshore process area usually needs a multispectrum IR (IR3) flame detector with heated optics, a stainless steel housing and marine type approval on top of its hazardous-location marking. Det-Tronics lists offshore production platforms and production ships as X3301 applications and offers the housing in stainless steel (316/CF8M Cast) with Type 4X and IP66/IP67 rating.

• Marine approvals: Det-Tronics lists US Coast Guard Approval No. 161.002/49/0 for the X3301, scoped to “a fire detection system meeting 46 CFR 161.002, as part of the Eagle Quantum Premier System”, and DNV type approval TAA00000V2 (the spec sheet gives MED certificate MED-B-9427, the manual MEDB00005C4); Honeywell’s FS24X Plus page lists “Maritime Type approved to ABS, Lloyds, BV, DNV”, although its 12/24 data sheet still marks them pending. Ask for the certificate that covers your configuration.
• Sunlight: direct and reflected sunlight gave no alarm in the X3301 FM tests at very high sensitivity, and Spectrex rates its 40/40C and 40/40D immune at any distance to indirect or reflected sunlight.
• Fog, rain and ice: IR is absorbed by water, so use heated optics, aim the detector at least 10 to 20 degrees down and keep a self-test such as the X3301 oi every 60 seconds.

Which explosion-proof flame detector should protect an aircraft hangar?

A hangar detector needs long range and must ignore friendly fires seen through open doors and avionics interference; Det-Tronics offers the explosion-proof X3301 with a Hangar Mode. Hangar Mode adds a seven to nine-second processing algorithm to ignore short-duration sources such as friendly fires from aircraft auxiliary power units.

• FM figures: at very high sensitivity with Hangar Mode, FM lists Avgas (1 x 1 foot) at 210 ft (64.0 m) in 9 s and, outdoors with pre-burn, Jet A (2 x 2 feet) at 300 ft (91.4 m) in 9 s.
• Codes: Det-Tronics lists NFPA 409 (Standard on Aircraft Hangars), NFPA 410 (Standard on Aircraft Maintenance), FM Global Datasheet 7-93 and UFC 4-211-01 among the requirements of the Authorities Having Jurisdiction (AHJ), and calls for validating performance during commissioning.

Which explosion-proof flame detector suits a gas turbine enclosure?

A turbine enclosure needs a detector that tolerates hot casings in view without delaying the alarm: the X3301 T-Low sensitivity is designed for elevated IR background in turbine enclosures, compressor engines, generators and heat exchangers, with no alarm delay.

• FM figures: T-Low is listed at 50 ft (15.24 m) in under 4 s for 1 x 1 foot n-heptane and 30 ft (9.1 m) in 3 s for a 32-inch methane plume.
• Fuels: Det-Tronics positions the X3301 for hydrocarbon fires from fuel, diesel or lube oil in gas turbines, and the X3302 for hydrogen and Syngas fuel fires.
• Maintenance: Det-Tronics recommends inhibiting a detector with an intense IR source in view before people work near it.

Which flame detector can see a hydrogen fire?

Hydrogen burns without carbon, and Det-Tronics says the X3301 should not be used for fuels without carbon such as hydrogen, sulfur and burning metals. Choose a detector with published hydrogen fire tests.

• Multispectrum IR for hydrogen: the X3302 is performance approved at 38 m (125′) for a 0.76 m (30″) hydrogen plume fire, the SharpEye 40/40C-M is rated 118 ft (36 m) for a 30 in (0.75 m) high plume, and the FS24X Plus 61 ft (18 m) for a 32 in plume.
• UV: hydrogen storage is a typical X2200 application.

How do current flame detectors compare on published data?

Values and approval strings as printed; all seven models also list FM 3260 and EN 54-10.

Where can you buy a flame detector in Houston, Texas, and what should you ask the supplier?

PE Energy Industrial Supply, 2700 Greens Rd H300, Houston, TX 77032 (281-310-0628, pesales@pe-energy.com), is an authorized Det-Tronics distributor and lists the X3301 multispectrum IR, X3302, X5200 UVIR, X9800 single frequency IR and X2200 UV flame detectors with mounting hardware. PE also lists the Spectrex SharpEye 40/40C-I, 40/40D-I and 40/40C-LB UV/IR and the Oldham Simtronics MultiFlame DF-TV7 and Spyglass SG50-F.

• Model status: Spectrex discontinued the SharpEye 40/40 series (last order date December 31st, 2021; 40/40I replaced by 40/40C-I or 40/40D-I, 40/40L/LB by 40/40C-LB or 40/40D-LB), and MSA states the FL4000H has been replaced by the FL5000.
• Emerson’s lines: its 40/40 certification document names Rosemount as manufacturer, and Emerson also sells the Rosemount 975 series (QuadSense IR3 and UV/IR models).
• Ask the supplier for: the design fuel and fire size, sensitivity setting, full model code with output option, approval marking and SIL version.

Where do these figures come from?

• Det-Tronics: X3301 spec sheet 90-1218, X3301 manual 95-8704, safety manual 95-8720, exida certificate DET 1108054 C001, weather note 77-1047, X5200 spec sheet and manual, X9800 spec sheet and manual, X2200 spec sheet and manual, flame brochure, gas turbine brochure, hangar safety sheet and aircraft hangars page.
• Spectrex and Rosemount (Emerson): 40/40C data sheet, 40/40D data sheet, 40/40C/D manual, certification information, Letter of Transition and the Rosemount 975 page.
• MSA: FL5000 operating manual and safety manual, and the FL5000 page (data sheet, certificates and selection guide) and FL4000H page.
• Honeywell: FS24X Plus page, data sheet, FM performance appendix, user manual, safety manual and brochure, and the FSL100 technical handbook and page.

Summary: how to choose a flame detector

• Match the technology to the fuel: multispectrum IR for hydrocarbons, UV or a dedicated detector for hydrogen and other fuels without carbon.
• Compare range only at the same fire: fuel, size, sensitivity and response time belong with every distance.
• Insist on self-testing, heated optics: a dirty or iced window silently cuts coverage.
• Copy approvals and SIL scope from the label: marking, gas groups and SIL version are separate checks.
• Check the model is still sold: the SharpEye 40/40I, 40/40L/LB and MSA FL4000H have been replaced.
• Buy from an authorized distributor that quotes the full model code: PE Energy Industrial Supply in Houston, TX is authorized for Det-Tronics and lists the X3301, X3302, X5200, X9800 and X2200.

Related selection guide: open-path gas detector selection.