Triple IR (IR3) Flame Detectors

What Is an IR3 Flame Detector?

A large share of the energy released by a hydrocarbon fire is emitted as infrared radiation. Because of the emission bands of hot carbon dioxide and water vapor, the spectral distribution of this radiation follows a characteristic pattern. Multi-spectrum IR flame detectors decide whether a fire is present by comparing this pattern with those of non-flame sources such as the sun, hot metal surfaces or light fittings.

In the approach known in the industry as triple IR (IR3), the detector does not depend on a single IR band but evaluates several narrow bands together. The standard hydrocarbon variant of the detector described on this page works with four IR bands between 4 µm and 5 µm, while the variant with hydrogen fire detection uses four IR bands spread between 2 µm and 5 µm. The ratios between the bands, the flicker behavior of the radiation and the persistence of the signal over time are processed together to limit the effect of interference sources.

Because IR3 technology operates only in the infrared region, it is generally less sensitive to the smoke and oil vapor that weaken UV radiation, and it usually achieves longer detection ranges for hydrocarbon fires. The same detector family also includes variants that combine ultraviolet and infrared channels; where very fast response at short distances or special fire types such as silane are the priority, UV/IR flame detectors can be evaluated as well.

How Multi-Band IR Flame Detection Works

The fire decision of an IR3 detector depends on spectral ratio and time-based analysis steps all returning a positive result:

1.      Separating radiation with narrow-band filters: Infrared radiation entering through the detector window is directed to sensors fitted with narrow-band filters tuned to different wavelengths. One band is positioned on the hot carbon dioxide emission typical of a hydrocarbon flame, and the others on reference regions around it.

2.      Calculating spectral ratios: In a flame, radiation in the carbon dioxide band is markedly higher than in the reference bands, whereas sources such as hot surfaces, the sun or lamps spread their energy more evenly across the spectrum. The ratios between the bands turn this difference into a numerical criterion.

3.      Flicker and persistence analysis: Turbulent combustion causes an irregular, characteristic flicker in radiation intensity. In addition to the ratio criterion, the detector examines this time-dependent behavior; depending on the selected sensitivity and response mode, the signal must carry a fire signature for a certain period.

4.      Applying the sensitivity and response mode: One of six sensitivity levels and a standard, very fast or high-speed (explosion detection) response behavior are configured according to the risk profile of the application. In standard mode, a fire at 40 m is typically detected in under 2 seconds and a fire at 90 m typically in 10 seconds.

5.      Continuous self-monitoring and output: An infrared built-in test continuously verifies the integrity of the optical path and the electronics, and a field of view integrity test helps reveal contamination or obstructions in front of the window. Status information is reported via relays, stepped 0–20 mA, analog voltage, HART and RS-485 Modbus.

Extended Spectral Design for Hydrogen Fires

Because a hydrogen flame contains no carbon, it produces no significant emission in the carbon dioxide band and is hard to see with the naked eye in daylight. The variant with hydrogen fire detection is configured with four IR bands spread between 2 µm and 5 µm so that it also evaluates radiation from water vapor. For this variant the detection range for a hydrogen plume fire 0.75 m high and 0.25 m wide is 50 m; the field of view is 90° × 90° for hydrogen and 80° × 80° for other fuels.

Discriminating Hot CO₂ Sources

Hot CO₂ sources without a flame, such as engine exhausts, furnace stacks or hot process gases, can produce flame-like radiation in the carbon dioxide band. For applications where such sources are within the field of view, an enhanced hot CO₂ discrimination option can be selected for the standard hydrocarbon variant.

Infrared detection also depends on line of sight. Detection performance varies with fuel type, flame size, the detector’s angle to the flame axis and mounting geometry; the fact that effective detection range decreases toward the edges of the field of view must be taken into account in the coverage assessment.

Key Features

·         Long detection range: Detection up to 90 m for gasoline and n-heptane pan fires and up to 63 m for diesel, kerosene and jet fuels makes it possible to monitor large open areas.

·         Three response modes: Standard response, a very fast mode typically under 1 s at 30 m and a 50 ms explosion detection mode via the analog voltage output can be selected to suit the application.

·         Six sensitivity levels: Detection sensitivity can be set in six steps according to the size of the protected area and the density of interference sources.

·         Wide field of view: The standard hydrocarbon variant covers 100° horizontally and 95° vertically; a field of view limiter accessory can be used to exclude unwanted zones.

·         Field of view integrity test and infrared built-in test: Continuous verification of the optical path and electronics helps ensure that conditions impairing detection, such as window contamination or blockage, are reported as faults.

·         Two-mode heated optics: Low-power and standard-power heater modes allow energy consumption to be balanced against optical protection according to the risk of icing and condensation.

·         Universal wiring: A single 17-terminal wiring arrangement removes the need to choose a separate order variant for each output combination.

·         Internal event recorder: Past alarm and fault events are stored in the device, which makes post-incident review and maintenance analysis easier.

·         Factory calibration: The detector is shipped factory calibrated and is adapted to the application on site by setting its configuration parameters.

·         Two housing options: Electropolished 316 stainless steel or polyurethane-painted aluminum with a copper content below 1% can be selected.

Technical Specifications

The values below are typical data for the standard hydrocarbon variant and the variant with hydrogen fire detection in IR3 technology. Detection ranges refer to the highest sensitivity setting and a 0.1 m² pan fire; final values should be confirmed at project stage for the selected variant and configuration.

Hydrogen and ammonia fire values apply only to the variant with hydrogen fire detection; no detection value is defined for these fuels for the standard hydrocarbon variant. On site, wind, flame size and the detector’s angle to the flame axis change the effective range.

Key Advantages

·         Efficient coverage of large areas: The long detection range allows open process areas and tank farms to be covered with fewer detectors; the final number is determined by a layout assessment.

·         Detection continuity in smoke and dirty atmospheres: Because no UV band is used, detection performance is less affected in environments where dense smoke or oil vapor attenuates UV radiation.

·         Strong resistance to false alarms: Spectral ratio analysis, flicker evaluation and the optional hot CO₂ discrimination limit nuisance alarms that sources such as sunlight, hot surfaces and exhaust gases could otherwise cause.

·         Suitability for extreme climates: An operating range of –60 °C to +85 °C, two-mode heated optics and IP68 protection make use possible on sites ranging from arctic regions to hot desert climates.

·         Post-incident traceability: The internal event recorder makes the alarm and fault history available for review, supporting root cause analysis and maintenance decisions.

·         Infrastructure-independent integration: Relay, stepped current, analog voltage, HART and RS-485 Modbus outputs make it easier to integrate with existing fire and gas systems, PLC or DCS infrastructures.

·         Suitability for functional safety projects: Thanks to its SIL 3 compatible design, the detector can be evaluated for functions with a high safety integrity target; the loop itself still has to be verified on its own.

Application Areas

IR3 flame detectors are used in industrial and commercial areas that require long-range flame detection with good resistance to false alarms:

Oil and Gas Facilities and Pipelines

Used for long-distance monitoring of large areas at onshore and offshore production facilities, compressor and pump stations and pipeline installations.

Chemical and Petrochemical Plants

Monitors units that process flammable chemicals such as solvents, acrylates and vinyl acetate, with detection ranges of up to 75 m for these materials.

Tank Farms and Fuel and Gas Storage

Installed on pole or tilt brackets to cover pan fire scenarios at tank perimeters, loading islands and fuel and gas processing and storage areas.

Hydrogen Production, Hydrogenation and Fuel Cells

The variant with hydrogen fire detection is intended for detecting hard-to-see hydrogen flames in hydrogenation units of refining, food and chemical processes and in hydrogen fuel cell facilities.

Vehicle Battery Charging Stations and Automotive

A defined detection range for a single lithium-ion battery cell fire enables early flame detection in battery charging areas and automotive production plants.

Power Generation Facilities

Used to monitor hydrocarbon fire risks in fuel preparation, turbine and auxiliary system areas.

Explosives, Munitions and Fertilizer Plants

In production and storage areas with fast-developing fire and explosion scenarios, the high-speed response mode can be evaluated against the application requirements.

Hazardous Materials Storage, Mining and Aerospace

Adds a flame detection layer in hazardous materials storage areas, warehouses, mining facilities and aerospace manufacturing areas.

How to Select an IR3 Flame Detector

Choosing the right variant and configuration determines how the detector actually performs on site. Before a technical assessment, it helps to clarify the following topics:

Fuel and Fire Type

·         Whether the fuels in the protected area are hydrocarbons, alcohols, solid combustibles or hydrogen — hydrogen and ammonia fires require the variant with hydrogen fire detection

·         For special risks such as silane or metal fires, a separate review of IR3 suitability and an assessment of UV/IR-based solutions

·         Presence of hot CO₂ sources such as engine exhausts or furnace stacks, and the need for the hot CO₂ discrimination option

Distance, Field of View and Coverage

·         Smallest fire that must be detected and how far from the detector it could occur

·         Field of view by variant (100° × 95° or 80° × 80°) and the shorter effective range toward the edges of the coverage area

·         Tanks, equipment and platform structures that interrupt the line of sight; use of a field of view limiter for unwanted zones

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

Response Behavior and Alarm Logic

·         Which of the standard, very fast or explosion detection modes suits the risk scenario

·         Setting the sensitivity level according to area size and interference sources

·         Compatibility with extinguishing-system release and voting logic

Ambient Conditions and Power Budget

·         Heater mode selection according to ambient temperature and the risk of icing and condensation

·         Current consumption ranging from 60 to 280 mA depending on heater mode, reflected in the supply and cable cross-section calculations

·         Stainless steel housing for salt-laden or corrosive atmospheres; whether an air shield and protective cover are needed

Integration and Approvals

·         Signal format required by the control system: relay, stepped 0–20 mA, analog voltage or digital communication

·         Hazardous area approval required in the project country (ATEX/IECEx/UKCA, USA–Canada, INMETRO, EAC, China)

·         Target safety integrity level for the safety instrumented function and the certificate documentation required

If a gas leak risk also exists in the process area, it is advisable to plan flame detection together with open path gas detectors and infrared point gas detectors. Detector placement should be assessed on the basis of the plant’s risk analysis and the applicable design criteria.

Hazardous Area Approvals and Conformity Standards

The approval options offered for the IR3 flame detector, depending on the ordered configuration, and the applicable conformity standards are summarized below.

The scope of performance approvals and the details of hazardous area marking may vary with the selected variant, housing material and approval code, so we recommend obtaining current certificate copies for project documentation.

IR3 Flame Detection Solutions from TLY Enerji

The coverage benefit of long-range IR3 detectors only materializes on site with correct positioning and correct configuration. That is why TLY Enerji starts with an application review that considers the geometry of the protected area, the fuel inventory, likely interference sources and climatic conditions together; choices such as the hydrocarbon or hydrogen variant, the sensitivity level and the response mode are based on the results of this review.

Our engineering team provides support in matching the output and communication structure to the fire and gas control system, PLC or DCS; calculating the power budget according to heater mode; preparing project documentation; planning function tests with a flame simulator during commissioning; and using event log data in maintenance processes. We also offer an engineering opinion when detector layout alternatives are reviewed, in line with the plant’s risk analysis.

Frequently Asked Questions

What is an IR3 flame detector?

An IR3 flame detector is a multi-spectrum optical fire detector that examines the infrared radiation of a flame in several narrow bands at the same time. By comparing the radiation in the carbon dioxide emission band of the flame with the surrounding reference bands, it distinguishes a fire from sources such as sunlight, hot surfaces and lighting. It is used especially to detect hydrocarbon fires from long distances in large open areas.

How does a multi-band IR flame detector work?

Radiation entering the detector is split between sensors with narrow-band filters tuned to different wavelengths. The ratios between the bands are compared with the characteristic spectral distribution of a flame, and the flicker frequency and persistence of the radiation are evaluated as well. When all criteria confirm a flame signature for the selected sensitivity level and response mode, an alarm is generated and reported via the relay, current, voltage or digital outputs.

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

An IR3 detector works with infrared bands only and offers a detection range of up to 90 m for a gasoline or n-heptane pan fire. For the UV/IR variants of the same family this value is 28 m; on the other hand, UV/IR technology can respond very quickly, in the order of 20 ms for a flash fire at 3 m, and can cover special fire types such as silane. The choice should be based on distance, fire type and interference sources.

Can an IR3 detector detect hydrogen fires?

Because a hydrogen flame produces no carbon dioxide, the standard hydrocarbon variant is not suitable for hydrogen fires. The variant with hydrogen fire detection uses four IR bands between 2 µm and 5 µm and can detect a hydrogen plume fire 0.75 m high and 0.25 m wide at a distance of 50 m. In this variant the field of view for hydrogen is 90° × 90°.

Why does detection range vary with fuel type?

Each fuel differs in combustion temperature, flame size, soot formation and carbon dioxide and water vapor emission, which changes the intensity and spectral distribution of the radiation reaching the detector. For example, the detection range is 90 m for gasoline, but 55 m for methanol and 34 m for paper. On site, wind, flame size and the detector’s angle to the flame axis also affect the effective range.

How are sensitivity and response mode selected?

Sensitivity is chosen from six levels according to the size of the protected area and the density of interference sources; higher sensitivity gives a longer range but calls for a more careful review of interference risks. For the response mode, the standard mode is considered for general fire detection, the very fast mode for rapidly developing fires, and the high-speed mode for special scenarios that require explosion detection via the analog voltage output.

How is an IR3 flame detector tested?

The detector’s infrared built-in test continuously verifies the optical path and the electronics, and the field of view integrity test helps detect window contamination or blockage. In periodic field tests, a hazardous-area-approved flame simulator matched to the relevant variant is used to confirm the alarm chain with no real flame required. Window cleaning and test intervals should be planned according to the plant’s maintenance procedures.

How are icing and condensation prevented in cold climates?

The detector has two-mode heated optics, with low-power and standard-power settings, and can operate down to –60 °C. Heating stops ice and condensation from forming on the window and helps preserve detection performance. Because consumption rises to 280 mA in alarm in the standard heater mode, the supply capacity and cable cross-section should be planned for this value.