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Ammonia Gas Detection

March 28 2016
Ammonia Gas Detection
system codes and design specifications
March 28th, 2016

Following is a discussion of ammonia detection system design for facilities utilizing ammonia refrigeration systems.
There are numerous codes that may affect the system design, including IIAR-2A, ASHRAE 15, NFPA-1, UMC, IFC, and IMC. In addition to these codes, many insurance carriers impose their own requirements to mitigate the risk of loss of life and product in a facility. What follows is a system design that respects all of the above mentioned influences, choosing the most conservative approach where there are differences in code.


Table 1: Ammonia Detection System Overview
Room Sensor Action
Compressor Room
(minimum 2)
GG-NH3-250
25 ppm - Alarm to monitored location
25 ppm - Horn Strobe outside each entrance and inside room
150 ppm - Emergency Ventilation
Compressor Room
(minimum 1)
GG-NH3-2%
10,000 ppm - Redundant Emergency Ventilation
20,000 ppm - De-energize pumps, compressors, and normally closed valves
Vent Line GG-VL-NH3 10,000 ppm - Alarm to monitored location
Refrigerated Areas GG-NH3-100
25 ppm - Alarm to monitored location
35 ppm - Close liquid and hot gas solenoid valves
Packaged Systems GG-NH3-100
25 ppm - Alarm to monitored location
25 ppm - Horn Strobe inside room
Machinery under 100 HP
and Equipment Pits
(not in Machine Rooms)
GG-NH3-100
25 ppm - Alarm to monitored location
25 ppm - Close liquid and hot gas solenoid valves
25 ppm - Horn Strobe inside room
25 ppm - De-energize pumps, motors, and non-emergency fans
25 ppm - Emergency Ventilation




Ammonia Compressor Room (0-250 ppm NH3 sensors)
Codes require audio-visual indication inside the compressor room and outside each entrance to the compressor room at 25 ppm. From the gas detection control panel or PLC, the warning outputs can be set at 25 ppm to activate a horn / strobe unit inside the engine room and outside each entrance. Entrance monitor display units can be located outside each doorway to warn personnel of ammonia concentrations prior to entry.

Codes require emergency ventilation at 150 ppm. The alarm setpoints can be set at 150 ppm and trigger the emergency vent fan starter.

The compressor room is the highest risk location in most plants. It has the most potential leak sources and the most ammonia available to build up to disastrous concentrations. Using a minimum of two 0-250 ppm sensors for complete coverage and redundancy is necessary. Use two 0-250 ppm ammonia gas sensors in Engine Rooms 4,000 square feet or less. Install an additional sensor for each additional 2000 square feet. Locate sensors in the breathing zone – 5 feet off the floor. Locate one sensor below the ventilation fan so it samples airflow from throughout the room when the fan is on. Locate other sensor(s) evenly distributed throughout the room.


Ammonia Compressor Room Shutdown (0-2% NH3 sensor)
In the compressor room, codes also require shutdown of compressors, pumps, and normally closed solenoid valves at a very high concentration (20,000 ppm is industry standard). The alarm output can be used to shut down at 2% (20,000 ppm). For redundancy at no cost, the warning output can be used to also trigger emergency ventilation at 1% (10,000 ppm). Use one 0-2% sensor located 5 feet off the floor below the emergency ventilation fan so it samples airflow from throughout the room in an emergency condition. Note that a sensor in this range cannot be used at the lower concentrations covered by the 0-250ppm sensor.


Ammonia Vent Line (0-1% NH3 sensor)
Vent line sensors are used to provide an alarm to a monitored location in the event of a safety relief valve opening from an overpressure condition. This alerts operators to discharges of ammonia to atmosphere through the vent line so they can take action to mitigate the release. An alarm setpoint of 1.0% (10,000 ppm) is recommended for this application to minimize alarms due to "weeping” relief valves. Locate vent line sensors outdoors, 3 ft off the roof, utilizing the provided mounting kit with the tee test-port facing down.


Ammonia Refrigerated Rooms (0-100ppm NH3 sensor)
In refrigerated rooms, codes require alarming to a monitored location. Some insurance companies require shutdown of liquid feed and hot gas solenoids in the event of a leak (but the major codes currently do not). Use 0-100 ppm sensors in these rooms. This range gives the best accuracy at very low concentrations which is appropriate in these unrestricted areas. From the gas detection panel or PLC, the warning output can alarm to a monitored location at 25 ppm. Additionally, the alarm output can be used to shut down the liquid feed and hot gas solenoids at 35 ppm to mitigate the leak.

Locate sensors in the breathing zone – 5 feet off of the floor. Quantity of sensors should be selected to have a sensor located within 30 horizontal feet of each leak source (one sensor located between 2 evaporators could cover them both if they are 60 feet apart). In large, open cold storage warehouse rooms where this results in more than 3 sensors in a room, distances can reasonably be relaxed to 50 horizontal feet from a potential leak source, with a minimum of 3 sensors.


Machinery under 100 HP not in Machine Rooms, and Equipment Pits
Where an ammonia refrigeration system or equipment is installed outside of a machinery room, the area containing the system or equipment shall comply with the following. At 25 ppm, alarm to a monitored location, close liquid feed and hot gas solenoid valves, activate audio/visual devices inside the area, activate emergency exhaust and de-energize all pumps, motors and non-emergency fans.

Use 0-100 ppm sensors in these rooms. This range gives the best accuracy at very low concentrations which is appropriate in these areas. Locate sensor(s) in the breathing zone – 5 feet off of the floor.


Packaged Systems
Packaged systems and equipment shall comply with the following. At 25 ppm, alarm to a monitored location and activate audio/visual devices inside the area.

Use 0-100 ppm sensors in these areas. This range gives the best accuracy at very low concentrations which is appropriate in these areas. Locate sensor(s) in the breathing zone – 5 feet off of the floor.


Sensor Mounting Height
There is much confusion in the industry concerning the best height to mount ammonia sensors. This is because there are valid reasons for different heights. Codes simply say "locate where refrigerant from a leak is expected to accumulate”. Ammonia vapor is lighter than air so vapor leaks will rise to the ceiling in normal conditions. A liquid leak will drop to the floor and if large enough can cool down a room so quickly that high concentrations are found on the floor with very low concentrations at the ceiling. In refrigerated areas there is normally enough air flow from evaporator fans to mix the refrigerant fairly well in the room. In all locations, 25 ppm is the first alarm point and this is intended for personnel protection. To protect the people, the sample should be representative of what they are breathing – 5 feet off of the floor. Most importantly, the sensor needs to be easily accessible for the required 6-month calibration and output testing. An untested safety system only takes a few years to become a non-working safety system. The breathing zone - 5 feet off of the floor is the best height to satisfy all of the above concerns.


Gas Detection Panel (or PLC)
The gas detection system should be powered with a dedicated branch circuit from an emergency generator backup system that can operate the system in the event of a power outage. An uninterruptable power supply (UPS) that can run the system for a few minutes during the transition to emergency generator power should be utilized. All wire runs should be supervised with the controller indicating a fault if communication with a sensor is lost. Loss of power to the system should send a fault indication to a monitored location.

Any alarm condition should send a signal to a monitored location. This can be in the facility such as a control room or guard shack. It can be a building monitoring company, an auto-dialer, or other notification system that notifies responsible personnel 24/7.

All output functions must be configured to latch, so even if ammonia concentrations fall below the setpoint, a manual reset is required under the supervision of a qualified operator. This is necessary to protect against repeating a leak scenario that has been successfully detected and mitigated.


CO2 Cascade systems
For CO2 cascade systems, ammonia and CO2 detection are both required in the compressor room which contains the ammonia system and the cascade heat exchanger. CO2 detection is required instead of ammonia detection in refrigerated and process areas. Detection system design and output functions are similar with the difference being the CO2 sensor selected, warning setpoints at 0.5% (OSHA 8 hour TWA) and alarm setpoints at 1.0%. One controller can support a combination of ammonia and CO2 sensors. One caveat to keep in mind is that unlike ammonia, CO2 is always present in air, and concentrations can build up to these levels in a facility from sources other than a leak in the refrigeration system. Common examples are dry ice usage and normal personnel respiration in a non-ventilated room. CO2 sensors should be mounted in the breathing zone – 5 feet off of the floor.


Specifications:

Table 2: Equipment Table
Part Number Description Application
GG-6 Six channel controller
GG-XM Eight channel expansion module
GG-EM Entrance Monitor Outside Compressor room doorways
UPS-1000VA-LCD Uninterruptible Power Supply Backup power for GG-6
SHA-24 Horn/Strobe assembly 24vdc Audio Visual
GG-NH3-100 0/100 ppm electrochemical sensor Refrigerated areas
GG-NH3-250 0/250 ppm electrochemical sensor Compressor Room
GG-NH3-2% 0/2% catalytic bead sensor Compressor Room Shutdown
GG-VL-NH3 0/1% vent line sensor HP relief header, above roofline
GG-CO2-3% 0/3% infrared sensor CO2 refrigeration systems


Table 3: Warning and Alarm Setpoints Table
Room Warning/Alarm setpoints
Refrigerated Areas 25 ppm / 35 ppm
Compressor Room (0-250 ppm) 25 ppm / 150 ppm
Compressor Room Shutdown (0-2%) 1.0% / 2.0%
Vent Line 1.0%
Carbon Dioxide refrigerated area 0.5% / 1.0%


1. Equipment
    a. Equipment notes
        i. All controllers and sensors shall be manufactured by Calibration Technologies, Inc. - Phone number 866- 394-5861.
        ii. See Equipment table for part numbers and function descriptions.
        iii. See Warning and Alarm setpoints table for recommended setpoints.

    b. Controller
        i. Provide a GG-6 controller and necessary Expansion Modules to monitor all fixed sensors. The controller shall be equipped with programmable alarm relays to activate external horn/strobes, exhaust fans, monitoring systems, and shut down equipment.
        ii. The controller shall provide three alarm setpoints per channel.
        iii. The controller and expansion modules shall provide 4/20 mA signal inputs.
        iv. The controller and expansion modules shall provide +24 Vdc to power all connected sensors.
        v. The controller shall provide an LCD operator interface for simple menu-driven programming.
        vi. The controller shall provide a watertight enclosure to protect electronics and allow for outdoor installations where necessary.
        vii. The controller shall provide a horn relay which is silenceable from front panel silence key.
        viii. The controller shall provide an alarm log to record and store all events.
        ix. The controller shall provide a calibration mode which locks relay outputs for sensor maintenance and calibration.
        x. Controller shall supervise wire runs and indicate a fault if communication with sensors is lost.
        xi. Power controller with dedicated branch circuit using Uninterruptable power supply (UPS) backed up by emergency generator to provide 24 hour operation in the event of a power outage.

    c. Entrance Monitors
        i. Provide a GG-EM entrance monitor outside each compressor room entrance.
        ii. Entrance monitor shall terminate 4-20 mA signal from sensor and retransmit same to controller.
        iii. Entrance monitor to provide a bargraph display to warn operators of ammonia concentration present prior to entering compressor room.
        iv. Entrance monitor shall have on-board 10 amp relay.
        v. Entrance monitor shall have potted electronics to protect circuit board and components from moisture and corrosion.
        vi. Entrance monitor shall have a polycarbonate enclosure to prevent corrosion.
        vii. Entrance monitor shall have a linear 4/20 mA output signal.

2. Sensors
     a. Compressor Room 0-250 ppm
        i. Provide (2) GG-NH3-250 ammonia gas sensors in Compressor Rooms 4000 square feet or less. Install an additional sensor for each 2000 square feet.
        i. Locate sensors in the breathing zone – 5 feet off the floor.
        ii. Locate one sensor below the continuous ventilation fan so it samples airflow from throughout the room.
        iii. Locate other sensor(s) evenly distributed throughout the room.
        iv. The sensor shall have potted electronics to protect circuit board and components.
        v. The sensor shall have a polycarbonate enclosure to prevent corrosion.
        vi. The sensor shall provide a temperature controlled enclosure for use in any environment for improved cell life.
        vii. The sensor shall have a linear 4/20 mA output signal.

    b. Compressor Room Shutdown 0-2%
        i. Provide (1) GG-NH3-2% ammonia gas sensor for each Compressor Room.
        ii. Locate sensor 5 ft off the floor below the emergency ventilation fan so it samples airflow from throughout the room.
        iii. The sensor shall have potted electronics to protect circuit board and components.
        iv. The sensor shall have a polycarbonate enclosure to prevent corrosion.
        v. The sensor shall provide a temperature controlled enclosure for use in any environment for improved cell life.
        vi. The sensor shall have a linear 4/20 mA output signal.

    c. Vent Lines
        i. Provide (1) GG-VL-NH3 ammonia vent line sensor for each high-pressure relief line discharge to atmosphere.
        ii. Install vent line sensor utilizing supplied mounting kit. Locate outdoors, 3 feet off of the roof. Install utilizing supplied mounting kit with tee test port pointed down.
        iii. The sensor shall have potted electronics to protect circuit board and components from moisture and corrosion.
        iv. The sensor shall have a stainless steel enclosure to prevent corrosion.
        v. The sensor shall have a linear 4/20 mA output signal.

    d. Ammonia refrigerated areas
        i. Provide GG-NH3-100 ammonia gas sensors near evaporators, valve groups, and other equipment with sensors installed no further than 30 horizontal feet from the potential leak source (50 feet if more than 3 sensors in a room).
        ii. Locate sensors in the breathing zone – 5 feet off of the floor.
        iii. The sensor shall have potted electronics to protect circuit board and components from moisture and corrosion.
        iv. The sensor shall have a polycarbonate enclosure to prevent corrosion.
        v. The sensor shall provide a temperature controlled enclosure for use in any environment for improved cell life.
        vi. The sensor shall have a linear 4/20 mA output signal.
    e. Carbon Dioxide refrigerated areas
        i. Provide GG-CO2-3% carbon dioxide gas sensors near evaporators, valve groups, and other equipment with sensors installed no further than 30 feet from the potential leak source (50 feet if more than 3 sensors in a room).
        ii. Locate sensors in the breathing zone – 5 feet off of the floor.
        iii. The sensor shall have potted electronics to protect circuit board and components from moisture and corrosion.
        iv. The sensor shall have a polycarbonate enclosure to prevent corrosion.
        v. The sensor shall provide a temperature controlled enclosure for use in any environment for improved cell life.
        vi. The sensor shall have a linear 4/20 mA output signal.



ANSI / IIAR 2-2014 ASHRAE 15-2013 NFPA 1-2015 UMC - 2015 IFC - 2012 IMC - 2012
General Comply with IIAR2, UMC and ASHRAE 15 Ammonia exception, comply with IIAR2, IIAR3, and IIAR5 Comply with IMC - 2012 Comply with IIAR2, ASHRAE 15, and IFC-2012
Alarm signal to monitored location 25 ppm Yes "Approved location"
Machine Room De-energize compressors, pumps, & NC valves 40,000 ppm or upper limit of detector 40,000 ppm or upper limit of detector 40,000 ppm or upper limit of detector
Machine Room Audio Visual Alarms inside room and outside each entrance 25 ppm 1,000 ppm Manual reset inside machine room 1,000 ppm 25 ppm* "Approved location"
Machine Room Activate emergency ventilation 150 ppm 1,000 ppm 1,000 ppm 1,000 ppm
Power and Supervision Dedicated branch, UPS or backup generator. Trouble signal indicating fault to monitored location Dedicated branch, 24 hour UPS or backup generator. Trouble signal indicating fault in system
Machine Room concentration display Suggested
Refrigerated Areas 25 ppm, alarm to monitored location 1,000 ppm
Packaged Systems 25 ppm, audio/visual and alarm to monitored location
Machinery under 100 HP not in machine room, and equipment pits 25 ppm, alarm to a monitored location, close liquid feed and hot gas solenoid valves, audio/visual devices inside the area, activate emergency exhaust and de-energize all pumps, motors, and non-emergency fans.





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