Ammonia (NH3) Gas Detectors for Industrial Applications
Experts in Ammonia Gas Detection
Ammonia (NH3) is a colorless gas or compressed liquid with an extremely pungent odor. It reacts violently with water and can seriously damage the skin, eyes and respiratory system. The gas has a density of 0.6 relative to air (1.0) and is flammable above 15% by volume in air.
The Threshold Limit Quantity for the storage of Anhydrous Ammonia is 10,000 lbs. (1,758 US gallons), and 20,000 lbs. (3,516 US gallons) for Ammonium Hydroxide.
The facility must comply with OSHA 29 CFR 1910.118, Process Safety Management (PSM) as well as the EPA Risk Management Program, 40 CFR 68, 69 FR 18819, April 9, 2004, Section 112(r)(7), when the storage capacity exceeds the Threshold limit value.
Ambient gas sensors are installed to warn of and quantify an Ammonia release. The gas monitors are usually placed near the loading rack and storage area, at the vaporizer, injection section and other locations near the Ammonia fluid handling equipment, having significant leak probability. Since Ammonia is lighter than air, sensors are normally positioned in the breathing zone, four to six feet above grade, or above the potential leak sources. Sensor spacing is determined by the specific hazard locations and the subsequent dangers presented to local personnel.
Ammonia Sensor ranges of 0-50 ppm, 0-100 ppm and 0-500 ppm can be supplied. Some users prefer to use a few 0-500 ppm sensors, as levels at or above the IDLH (300 ppm) will be indicated, and appropriate clothing and respirators can be selected by the emergency response team. An LEL sensor is often used in enclosed areas where there may be potential for a large Ammonia release and concentrations approaching the LEL (15%).
Mounting configurations for the gas sensors include placing the sensor remote from the transmitter, or drawing a sample from a remote or inaccessible location. The latter must include a flow switch to indicate sample system integrity. A special calibration adapter is supplied for the remote sensor option, so that calibration functions can be performed from the transmitter location.
Electro-chemical sensors have temperature limitations, which should be observed, or useful life will be compromised. Advanced organic Ammonia sensors, function over a range of –4° to 122° F (–20° to 50°C), but may fail in high humidity and high temperature. Heat shields are used to protect the sensor-transmitters from radiant heat off the flue work. Sample draw hardware can be used for high temperature areas.
Integrating a Process and Personnel protection gas detection system requires that the notification and control procedures mandated by Code and Law be followed, including Insurance Company mandates.
Compliance with these issues is simplified by using a Sensidyne Controller to process the gas sensor inputs, provide annunciation and supervisory control. A 4-Channel System is illustrated below. Up to 16 gas sensors may be accommodated by one Controller.
Ammonia Gas Detection Sensor Mounting Configurations
Gas sensors are located in the breathing zone (4 to 6 feet above floor) for gases similar in density to air, including Oxygen deficiency. For lighter than air gases, (Methane, Ammonia or Hydrogen), the sensors must be positioned within 12 inches of the ceiling or highest point of an enclosed area. Heavier than air gases like solvent vapors or Halocarbon refrigerants should have the sensors placed within 12 inches of the floor or lowest point in the enclosed area. Target gas density and potential leak sources should always be identified when configuring a gas detection system.
Gas sensors are often mounted remotely from the transmitter, which is normally kept at eye level. These situations arise due to gas density variations or difficult access locations. Tubing is run to a calibration adapter on the sensor assembly, so that routine calibrations can be performed from the transmitter. Other configurations include duct mounting, and drawing a sample from a remote or inaccessible location. The latter has a flow switch to indicate sample system integrity, as required by Code.
Careful attention to gas sensor placement, supervisory control functions and emergency response planning will produce a functional, accountable and low maintenance area monitoring system which complies with local codes and laws.