Flame Detectors
Principles, Design, Applications & Guidelines
What is a Flame Detector?
A flame detector is an optical safety device designed to identify and respond to the presence of a flame or fire. Unlike smoke or heat detectors which rely on physical particles or temperature changes reaching the sensor, flame detectors work by "seeing" the specific types of radiant energy (UV or IR light) emitted by a fire. This allows them to respond in seconds, making them essential for high-hazard environments.
Key Advantages
- • Speed: Responses in milliseconds to seconds.
- • Range: Detects fires from significant distances.
- • Versatility: Detects smokeless fires (e.g., Hydrogen).
Key Limitations
- • Line of Sight: Must see the flame; cannot see around corners.
- • Interference: Prone to false alarms from welding or sunlight.
- • Maintenance: Lens must be kept clean of oil and dirt.
Detection Principles & Comparison
Flame detectors are categorized by the spectrum of light they sense. Use the interactive tabs below to explore how each technology functions, or view the comparison chart to see performance trade-offs.
Ultraviolet (UV) Detectors
UV detectors sense the UV radiation (185-260 nm) emitted at the very instant of ignition. They are "blind" to sunlight but highly sensitive to the actual flame. Because they don't need heat to build up, they are the fastest responding detectors available, often reacting in under 10 milliseconds.
Best for: Hydrogen, Ammonia, Metal fires, and clean indoor environments.
Performance Trade-off: Speed vs. Reliability
A higher score indicates better performance (Faster Speed or Higher Immunity).
Applications & Selection Guide
Oil & Gas (Offshore/Onshore)
Why: High risk of hydrocarbon fires.
Choice: IR3 is preferred for its ability to ignore sunlight reflections on water and see through sea spray or oil mist.
Aircraft Hangars
Why: Large open spaces with high ceilings (stratification) make smoke detectors useless.
Choice: UV/IR or IR3 to monitor vast areas for sudden fuel spills under aircraft.
Chemical Storage
Why: Presence of non-carbon fuels like Hydrogen or Ammonia.
Choice: UV or UV/IR. Note: Standard IR detectors cannot "see" hydrogen fires.
Auto Manufacturing
Why: Paint spray booths and engine test cells.
Choice: IR3 is often used to look through paint mist, or high-speed UV/IR for engine tests.
Power Generation
Why: Gas turbines and hydrogen-cooled generators.
Choice: UV/IR provides a balanced approach for turbine enclosures.
Waste Management
Why: Deep-seated fires in large piles of waste.
Choice: IR3 provides wide area coverage and immunity to dust/debris in the air.
Installation & NFPA 72 Guidelines
Performance-Based Placement
According to NFPA 72 (Chapter 17), flame detectors are not placed by simple spacing rules (like smoke detectors). They are placed based on Field of View (FOV) analysis.
Critical Requirements
- 1 Cone of Vision: Ensure the hazard is within the detector's central cone (usually 90-120°). Sensitivity drops at the edges.
- 2 Line of Sight: There must be NO obstructions (beams, ducts, pipes) between the detector and the potential fire.
- 3 Interference: Do not aim detectors at known false alarm sources (e.g., windows facing the sun, welding stations).
Installation Best Practices
- ✓ Angle Downwards: Mount detectors at a downward angle (approx 45°) to prevent dust and oil from settling on the lens.
- ✓ Rigid Mounting: Prevent vibration. Vibrating mounts can cause false alarms in some IR detectors.
- ✓ Overlapping Coverage: Use multiple detectors looking at the hazard from different angles to eliminate shadows and blind spots.