INCORPORATING COLD CHAIN
TECHNICAL
Number and location of detectors
ANSI / IIAR 2
Alarm levels and function
Alarm notifications Maintenance Personal safety
USA
Two refrigerant leak detectors are required for each refrigeration machinery room with the purpose of triggering alarm and ventilation .
Various machinery room equipment like compressors , pumps and valves should be de-energised at a concentration not exceeding 40 000ppm .
Detector assignment : ( No 1 ) Alarm and normal mechanical ventilation system activation at the level not greater than the corresponding TLV- TWA *.
( No 2 ) Alarm and emergency mechanical ventilation system activation at the level not exceeding 1 000ppm .
* See personal safety section .
Visual and audible alarms triggered by the detectors for :
• Inside area of the refrigerating machinery room
• Outside each entrance to the refrigerating machinery room
Testing of ammonia detectors and the alarm system is required at intervals established at the facility .
Generally in accordance with the manufacturer ’ s recommendation or based on documented experience .
In case of missing recommendations , the equipment shall be functionally tested on an annual basis .
OSHA sets Permissible Exposure Limits as the legal requirement in the United States . They are published as 8h TWAs also for ammonia in 1910.1000 Z1 Table :
• TWA 50ppm and 35mg / m 3
OSHA has annotated the existing Z-Tables also with other recommended exposure limits , set by NIOSH and the ACGIH which are set at :
• TWA 25ppm
• STEL 35ppm
Table 2 : ANSI / IIAR 2 regulations for the USA
Number and location of detectors
Number not specified , location to ensure all equipment that contains refrigerant is properly monitored . Areas around pumps and compressors that suffer from shaft seal leaks have priority .
Alarm levels and function
Systems with more than 50kg that present an explosion or fire hazard :
350mg / m 3 ( 500 x 10-6 ( volume fraction )) for an alarm and when the emergency ventilation system should be started .
Up to a maximum of 7 070mg / m 3 ( 10 000 x 10-6 ( volume fraction )) whereupon the plant power supply shall be switched off thereby disabling the plant .
SANS 10147:2014
Table 3 : South African National Standard ( SANS ) 10147:2014 regulations
Alarm notifications Maintenance Personal safety
A detector shall , when activated by a refrigerant concentration that exceeds the pre-set limit , in addition to its other functions :
• Initiate an alarm that shall remain on until reset manually .
• The power supply to the detection system shall be from an independent source .
Generally in accordance with the manufacturer ’ s recommendation or based on documented experience .
South Africa
South Africa directives for Ammonia CAS No : 7664-41-7 is documented with :
• TWA 50ppm
• STEL 70ppm
ADDITIONAL CONSIDERATIONS REGARDING THE PHYSICAL LOCATION OF DETECTORS
As indicated by ANSI / IIAR 2 , ammonia as a vapour is lighter than air . It rises and diffuses simultaneously when released into the atmosphere , which indicates the location of the detectors above possible leak sources or at ceiling height . However , other conditions should be considered , such as those mentioned in EN 378-3 ( p . 9.2 ) indicating that the location of gas detectors should be planned with local airflow patterns taken into account – which are affected by ventilation sources or louvres . The possibility of mechanical damage or contamination should also be considered .
AMMONIA LEAK DETECTION SOLUTIONS
Aspirated monitoring Aspirated monitoring is considered a reliable ammonia detection method that contributes to personnel safety and plant operability . It protects equipment and people around a wide area due to its stable and selective sensing technology employed within an internal sampling system . Aspirated systems help to comply
Machinery room .
with EN 378 and ANSI / IIAR 2 . It ’ s important to consider an aspirated system that employs selective and sensitive ammonia leak detection with the ability to read down to at least 10ppm . Low level monitoring provides an early response to ammonia leaks . Unnecessary maintenance costs associated with calibration and exchange of sensors of multiple point detectors can be minimised by using a centralised sample draw system , with a single source Photoacoustic Infrared ( PAIR ) sensor technology or similar . Consider employing a system that is equipped with internal relays for fault , three levels of alarm and an external horn option for effective personnel warning as required by standards .
Point ammonia monitoring In addition to multiple-point monitoring for ammonia leaks , it is important to monitor specific locations in machine rooms with compressed system equipment , where a leak is likely to occur . One possible solution utilises electrochemical sensors , which address the challenges of short life and stability problems with traditional electrochemical cells . Consider a device that features ionic
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