Optical Fire Detection
Non-contact fire detectors have been manufactured for over 30 years. Originally, they were adapted from ultraviolet technology that had previously been used to look for “friendly fires” in the boiler industry. By reversing outputs and adding some optical fault detection components, a new generation of safety monitoring began. For years UV technology was used an many different fire detection applications. Certain drawbacks of the technology became evident along the way. Research into using sensors that could detect fire in the infrared part of the electromagnetic spectrum began to open up other detection possibilities. Soon, there were not only UV and IR detectors, but also UV/IR detectors, which utilized two detectors and improved resistance to optical false alarms. Multi-spectrum infrared technology using three separate IR sensors in one sensor followed soon after. The majority of optical fire detection today is made with some model of multi-spectrum IR detector. However, there are specific applications that still require the use of UV- or IR-only technology. Fire detection specialists can help in the proper selection of these.
In addition to monitoring fire and gas detection for refinery and pipeline processed in the oil and gas industry, here are a few other applications we specialize in:
Liquefied natural gas is 600 times denser than the gas form, making LNG more feasible than transporting natural gas. Planning a fire and gas detection system that can also provide suppression while immune to false alarms, addressing process hazards and local safety codes is critical.
Selecting Optical Fire Detectors
- Third-party approvals. Detectors are tested on different fires at various distances.
- Coverage areas with the greatest range and field of view. These offer cost savings.
- False alarm resistance to electromagnetic and radio interference, welding torches and reflective sunlight.
- Support. Proper selection / configuration of equipment, product warranty, and technical support are critical.
Here are three gas detection technologies that are used today:
- Acoustic Leak Detection for pressurized gas leaks, working instantly without contact, regardless of wind direction.
- Point Gas Detection for toxic or combustible gases uses electrochemical, catalytic, infrared or NTMOS types.
- Line-Of-Sight Infrared Detection for combustible gas “clouds” between two points up to 120 meters apart.
Selecting Gas Detection Technology
Here are four simple recommendations. Choose a gas detector with:
- Heated optics to improve operation in cold or damp environments
- Approved integral junction boxes and displays, installed without conduit seals.
- Rugged-weather baffles for protection against rain, dust and process splashing.
- Expert support on application and compliance can help owners build a safe, reliable system.
Gas Detector Placement – Three Recommendations
- With point-gas detection, it is best to place the detectors higher, toward the ceiling, when sensing for lighter-than-air gases; and lower, toward the floor, when sensing for heavier-than-air gases.
- Install detectors in areas where air flow will move a representative sample of ambient gases around the sensor. Often, this is near vents/duct-work.
- Look for the area(s) of highest risk – potential leak points, like valves, fittings/connections, pumps.
Gas Detector Placement – Specifics
Identification Of Flammable Vapors To Be Detected
It is necessary to always identify the flammable vapors of interest at the job site in order to determine the proper calibration gas setting for the combustible gas transmitter. In addition, the fire hazard properties, such as vapor density, flash-point, and vapor pressure should be identified and used to assist in selecting the optimum detector mounting location within the area.
Identification Of Detector Mounting Locations
First, determine the most likely leak sources and leak accumulation areas. Next, identify air current / wind patterns within the protected area. This is useful in predicting gas leak dispersion behavior. These two steps will help to indicate the optimum sensor installation points.
If the vapor of interest is lighter than air, place the sensor above the potential gas leak. Place the sensor close to the floor for gases that are heavier than air. For heavy vapors, typically locate the combustible gas sensor 2 to 4 cm above grade elevation. Air currents may cause a gas that is slightly heavier than air to rise under some conditions. Heated gases may also exhibit the same phenomenon.
The most effective number and placement of detectors varies depending on the conditions at the site. Also, locate detectors where they are accessible for maintenance. Locate transmitters where indicators can be easily seen. Mounting equipment near excessive heat / vibration sources should be avoided if possible.
Final suitability of locations should be verified by a job site survey. Gas detector area of coverage is a subjective evaluation, and may require long-term empirical data to confirm effectiveness. A typical rule of thumb is that one detector can cover a 900 square-foot area. However, this is subject to change depending upon specific application properties and requirements.