UV/IR Flame Detectors

What Is a UV/IR Flame Detector?

Fire detection in industrial plants depends on choosing correctly between heat, smoke and flame detectors. In open process areas, high-ceilinged hangars and wind-exposed sites, smoke and hot gases can disperse before they ever reach a detector. Flame detectors take a different approach: they sense the electromagnetic radiation released during combustion along a line of sight, so they do not have to wait for smoke or heat to travel to the device.

The UV/IR flame detector is the member of the optical detection family that combines two different spectral regions. Its ultraviolet sensor responds to the short-wave UV radiation emitted by excited molecules in the flame zone, while its infrared sensor responds to the band around 4.5 µm, where the hot carbon dioxide formed in hydrocarbon combustion radiates strongly. The electronics evaluate both channel signals in terms of frequency, intensity and duration, and an alarm decision is made only when both channels show flame characteristics at the same moment.

With this design, defined detection ranges are available not only for hydrocarbon fuels such as gasoline, n-heptane, diesel, jet fuel, LPG and methane, but also for methanol, isopropyl alcohol, polypropylene pellet and paper fires. UV/IR technology is a sensible choice where fast response at medium distances and false alarm immunity are needed together. For open areas that call for longer detection ranges, triple IR (IR3) flame detectors, which work with infrared bands only, can be considered as an alternative.

How UV/IR Flame Detection Works

In a UV/IR detector, the alarm decision is based on the joint evaluation of two independent spectral channels. The detection chain can be summarized in the following steps:

1.      UV channel: sensing short-wave radiation: The UV sensor is sensitive to the 0.185–0.260 µm range. Because this short-wave part of sunlight is largely absorbed in the atmosphere, radiation in this band is a strong indicator of a flame in open areas. A dedicated logic circuit built into the UV channel additionally helps to suppress alarms triggered by sunlight.

2.      IR channel: monitoring the carbon dioxide emission band: The IR sensor operates in the 4.4–4.6 µm range. Hot carbon dioxide released when hydrocarbon fuels burn produces a pronounced emission in this region, which makes the IR channel particularly responsive to hydrocarbon fuel and gas fires.

3.      Frequency, intensity and duration analysis: Turbulent combustion makes flames flicker in a characteristic way. The detector assesses the signal of each channel for frequency content, radiation intensity and persistence, in order to tell flames apart from non-flame sources such as steady hot surfaces or brief flashes.

4.      Channel coincidence and alarm decision: An alarm is generated when radiation is registered in the UV and IR channels at the same time. A time delay adjustable up to 30 seconds can be used to keep transient events from causing alarms; because this delay adds to the total response time, it must be taken into account when fire scenarios are assessed.

5.      Reporting status and diagnostic information: Alarm, warning and fault states are passed to the control system through relay contacts and a stepped 0–20 mA signal. Because the stepped current output reports IR-only and UV-only detection at their own current levels, operators can see remotely which channel has responded.

How the UV and IR Channels Complement Each Other

UV detection tends to respond quickly, but it can be affected by intense UV sources such as arc welding and lightning, and dense smoke, an oil film on the window or certain organic vapors can attenuate UV radiation. IR detection is more tolerant of smoke, yet hot surfaces and modulated radiation sources can produce signals in the IR channel. Requiring both channels to confirm at the same time reduces the likelihood that interference sources specific to either technology will cause an alarm on their own.

Sensing UV and IR radiation requires a direct line of sight. Structural obstructions between the detector and a potential fire location, dense smoke and a contaminated window all reduce detection performance; performance also depends on fuel type, flame size and mounting geometry and must be assessed separately for each application.

Key Features

·         Dual-channel UV/IR sensor design: Evaluating the ultraviolet and 4.5 µm infrared sensors together produces fast, confirmed alarms for hydrocarbon fires.

·         Automatic and manual built-in test: The built-in test (BIT) checks optical and electronic integrity at regular intervals and can also be started manually during maintenance. A test failure is reported separately at the 2 mA level on the current output.

·         Heated optical window: Window heating keeps snow, ice and condensation from building up on the optical surface, supporting continuous detection in cold and humid climates.

·         Three independent relay outputs: Volt-free SPST contacts with a 2 A / 30 Vdc rating serve the alarm, fault and auxiliary functions.

·         Stepped 0–20 mA status signal: Normal, warning, alarm, fault and BIT fault states, as well as IR-only and UV-only detection, are each sent at their own current level over a single analog line.

·         Configuration via HART and RS-485 Modbus: Sensitivity, delay and maintenance parameters can be read and changed over HART or RS-485 Modbus without a trip to the field.

·         Wide field of view: A 100° horizontal and 95° vertical field of view lets a single detector watch over a large volume.

·         Adjustable alarm delay: A delay adjustable up to 30 seconds allows alarm behavior to be adapted to areas where short transient events are frequent.

·         Stainless steel housing and mount: An electropolished 316L stainless steel housing and mounting bracket suit the corrosive atmospheres of offshore and chemical facilities.

·         High reliability: A minimum mean time between failures (MTBF) of 150,000 hours makes maintenance planning more predictable.

Technical Specifications

The values below are typical technical data for the UV/IR flame detector described on this page. Housing material, temperature option, wiring option and approval scope can vary with the ordered configuration, so final values should be confirmed at project stage.

Detection ranges are stated for the highest sensitivity setting and for defined test fires. On site, wind, flame size, fuel type, the detector’s angle to the flame axis and window cleanliness all change the effective range; the effective range generally decreases toward the edges of the field of view.

Key Advantages

·         Confirmed alarm decision: Requiring simultaneous detection in two different spectral regions makes it less likely that a single interference source triggers an alarm, helping to avoid unnecessary plant shutdowns and extinguishing-system releases.

·         Fast response to hydrocarbon fires: A typical response time of 5 seconds supports detection of liquid-fuel and gas fires before they grow and lets the control system act early.

·         Continuity in harsh weather: The heated window, wide operating temperature range and environmental tests covering salt fog, vibration and mechanical shock provide a sound basis for uninterrupted outdoor monitoring.

·         Remote diagnostics and easier maintenance: Stepped current levels, HART and RS-485 Modbus allow detector status, the responding channel and fault information to be monitored from the control room.

·         Flexible system integration: Offering relay, analog and digital outputs together makes it easier to connect the detector to different fire and gas panels, PLC and DCS infrastructures.

·         Suitability for functional safety projects: SIL 2 approval to IEC 61508 allows the detector to be considered for safety instrumented functions; SIL verification at loop level must still be carried out separately.

·         Recognized performance approvals: EN 54-10 and FM 3260 performance approvals help meet the flame detector performance requirements found in insurer and owner specifications.

Application Areas

UV/IR flame detectors are used wherever hydrocarbon fuels, solvents and combustible materials are processed or stored. The main application areas are:

Oil and Gas Facilities

Used to monitor liquid-fuel and gas fire risks around separators, pump and compressor packages in onshore and offshore process facilities. The stainless steel housing suits salt-laden marine atmospheres.

Chemical and Petrochemical Plants

Provides early flame detection in process units handling flammable solvents, monomers and intermediates; the hazardous area approval covers gas group IIC atmospheres.

Tank Farms and Fuel Storage

Positioned on pole or U-bolt mounting brackets to watch pan fire scenarios around tanks, at loading islands and at pump stations.

Aircraft Hangars and Aviation

Used in high-ceilinged hangars to detect jet fuel fires before a smoke layer forms; can also be considered for aerospace manufacturing areas.

Power Generation Facilities

Monitors areas with hydrocarbon fire risk, such as turbine and fuel preparation areas and fuel oil and gas supply systems.

Pharmaceutical, Paint, Polymer and Adhesive Processes

Contributes to early fire recognition in production areas that use alcohols and solvents, as well as in polymer pellet and adhesive processes.

Printing Plants and Warehouses

Adds a flame detection layer in printing facilities where paper, inks and solvents are present together, and in warehouses storing combustible materials.

Waste Disposal Facilities

Used to monitor fire scenarios that may involve different fuel types in the reception, storage and processing areas for combustible waste.

How to Select a UV/IR Flame Detector

Flame detector selection should be addressed together with the plant’s fire scenarios. For a technical assessment we recommend clarifying the following:

Fire Scenario and Fuel Type

·         Likely fuels: hydrocarbon liquids, gases, alcohols or solid combustibles

·         Minimum fire size to be detected and its greatest distance from the detector

·         Possibility of jet or plume fires caused by pressurized gas leaks

·         Presence of non-hydrocarbon fuels such as hydrogen — in that case detectors with a different spectral design must be evaluated

Coverage and Mounting Geometry

·         Field of view (100° horizontal, 95° vertical) and the reduced effective range at the edges of the area

·         Obstructions in the line of sight such as tanks, pipe racks, equipment and platforms

·         Need for critical areas to be seen by more than one detector from different angles

·         Mounting height, tilt angle and choice of tilt, duct or pole mounting bracket

False Alarm Sources and Ambient Conditions

·         Potential interference sources such as arc welding, lightning, hot surfaces and solar reflections

·         Risk of dense smoke, oil vapor or window contamination that could attenuate UV radiation

·         Snow, ice and condensation conditions; need for a weather protector or air shield accessory

·         Ambient temperature: standard –55 to +75 °C or optional –55 to +85 °C

Electrical Interface and System Integration

·         24 Vdc supply and a current budget that includes the heated window

·         Signal type expected by the control system: relay, stepped 0–20 mA (sink/source) or digital communication

·         Wiring option to be defined at ordering, bearing in mind that HART is available with the mA source wiring options

·         Alarm, fault and voting logic in the fire and gas control system

Approval and Safety Requirements

·         Hazardous area classification, gas group, temperature class and presence of combustible dust

·         Target SIL for the safety instrumented function

·         Whether the specification calls for EN 54-10 or FM 3260 performance approval

Detector placement and coverage should be assessed on the basis of the plant’s fire risk analysis and the applicable design criteria. Where the process area also carries a gas leak risk, we recommend planning the flame detection concept together with open path combustible gas detectors and infrared point gas detectors.

Hazardous Area Approvals and Performance Standards

The approvals and conformity standards defined for the UV/IR flame detector described on this page are summarized below.

The approval scope may vary with housing material, temperature option and ordered configuration. For project documentation, we recommend confirming the valid certificate copies separately at procurement stage.

UV/IR Flame Detection Solutions from TLY Enerji

At TLY Enerji we treat flame detection not simply as a device supply but as a safety layer that has to be designed around the plant’s fire scenarios. Our application review looks at the equipment to be protected, the likely fuel types, the expected flame size, the line of sight from candidate mounting points and the false alarm sources on site. On this basis we help customers make a technically justified choice between UV/IR and multi-band IR technology.

We support project teams in matching the output and wiring configuration of the selected detectors to the fire and gas control system, PLC or DCS; preparing signal lists and connection documentation; planning function checks with a flame simulator during commissioning; and setting up a periodic test program. For detector placement and coverage assessment, we provide engineering support aligned with the plant’s risk analysis and design criteria.

Frequently Asked Questions

What is a UV/IR flame detector?

A UV/IR flame detector is an optical fire detection device that monitors the ultraviolet and infrared radiation of a flame with two separate sensors. It raises an alarm when a flame signature is seen at the same time in the short-wave UV band and in the IR band around 4.5 µm. It is used in areas with a hydrocarbon fire risk, such as oil and gas facilities, chemical plants, tank farms and hangars.

How does a UV/IR flame detector prevent false alarms?

The detector only alarms when radiation is registered simultaneously in both the UV and IR channels. Sources that emit only UV, such as arc welding, or only IR, such as hot surfaces, therefore cannot trigger an alarm on their own. The signals are also analyzed for frequency, intensity and duration, a dedicated logic circuit in the UV channel limits the influence of sunlight, and a delay of up to 30 seconds can be set. Possible interference sources should nevertheless be reviewed at the layout stage.

What is the detection range of a UV/IR flame detector?

At the highest sensitivity setting and for a 0.1 m² pan fire, the detection range is 28 m for n-heptane and gasoline, 21 m for diesel, kerosene and isopropyl alcohol, and 17 m for methanol. For methane and LPG plume fires the value is 18 m. On a real site, the range varies with fuel type, flame size, wind, the detector’s angle to the flame axis and window cleanliness.

What is the difference between UV/IR and IR3 flame detectors?

A UV/IR detector combines one ultraviolet and one infrared channel and provides fast, confirmed detection at medium distances. IR3 detectors compare several narrow bands in the infrared region only; for hydrocarbon fires they generally offer longer detection ranges and are less affected by smoke and oil vapor that attenuate UV. The choice should be based on the fire scenario, the distance involved and the interference sources present.

What does a heated window do?

A heated optical window prevents snow, ice and condensation from building up on the window surface in cold and humid environments. Such deposits can attenuate the radiation reaching the detector from a flame and shorten the detection range, so heating is especially important on offshore facilities and in regions with severe winters. Current consumption rises while heating is active: allow for a maximum of 110 mA in standby and 160 mA in alarm.

Which outputs connect the detector to the control system?

The detector has three volt-free relays for alarm, fault and auxiliary functions, plus a stepped 0–20 mA output. The current output uses distinct levels, for example 4 mA for normal, 16 mA for warning and 20 mA for alarm. Optional HART communication is available with the mA source wiring options, and the RS-485 Modbus link is used for configuration and monitoring in computer-controlled systems.

How is a flame detector tested?

The detector checks its optical and electronic integrity periodically with an automatic built-in test, and a manual test can also be started. For field function tests, a flame simulator kit suited to the detector is used to verify the alarm chain without creating a real flame. Test intervals and acceptance criteria should be planned according to the plant’s maintenance procedures and the test requirements defined for safety instrumented functions.

Which hazardous area approvals does the UV/IR flame detector have?

The detector described on this page holds ATEX and IECEx approval for gas group IIC and temperature class T4, and group IIIC approval for combustible dust atmospheres. In North America, FM, FMC and CSA approvals allow use in Class I Div. 1 and Class II/III Div. 1 areas. On the performance side it carries EN 54-10 and FM 3260 approvals, and for functional safety an IEC 61508 SIL 2 approval.

How many flame detectors does an area need?

The number of detectors depends on the geometry of the area to be protected, the minimum fire size to be detected, the fuel type, obstructions and the voting logic in the control system. In critical areas, a common design approach is to have the same zone seen by more than one detector from different angles. The final number and positions should be set by a layout assessment based on the plant’s risk analysis and applicable design criteria.