INSTRUMENTATION & LEAK DETECTION
Fixed gas detection for ammonia safety standards compliance
Refrigeration systems using Ammonia are often considered cost-eff ective, energy-effi cient, and environmentally friendly. Ammonia has zero ozone depletion potential and zero global warming potential. However, ammonia is classifi ed as a B2 refrigerant under the ISO 817 classifi cation scheme, meaning it has higher toxicity and fl ammability than other A1 and A2L refrigerants. This article from MSA looks at compliance and safety standards for ammonia leak detection and how this helps avoid serious accidental injury or death.
absorption refrigeration that used water and ammonia. In the 1860s, ammonia was applied to artifi cial ice production in the United States. Now, ammonia refrigeration systems can be
A Table 1: EN 378-3 / ISO 5149-3 regulations for Europe
Number / Loca- tion of Detectors
One refrigerant detector is required as a minimum for each refrigeration machinery room and/or occupied space.
Note:
• Ammonia systems with charge greater than 500kg, require gas detectors within heat transfer circuit of indirect systems.
• Machinery rooms with compressors require a minimum of one detector placed over the compressor unit.
• Refrigerant pumps in any areas require a detector placed over or near the pumps.
Alarm Levels / Function
Ammonia system with charge greater than 50 kg require a gas detector to warn in case of fi re risk and for control purposes.
Alarming levels and actions:
(1st ) Pre-alarm -
Mechanical ventilation activated for concentrations not exceeding 500 ppm (EN) or 200 ppm (ISO).
(2nd) Main alarm – both refrigerating system and mechanical ventilation stopped, power supply to machinery rooms
Isolated automatically - for concentrations not exceeding 30,000 ppm.
Alarm Notifi cations EN 378-3 / ISO 5149-3
Visual and audible alarms triggered with both a loud beacon and a fl ashing lamp, within:
• Machinery room – warning inside and outside the machinery room. The alarm outside the machinery room may be installed in a supervised location.
• Occupied space – warning at least inside the occupied space.
Additional alarm system requirements for charges above 3,000 kg (EN) or 4,500 kg (ISO):
• User or owner responsibility is to ensure that a continuously attended station is provided as a central alarm station.
• Specialised personnel are required on site within 60 minutes of an alarm.
Testing of ammonia detectors is required at appropriate intervals established at the facility.
Correct functioning of alarms, mechanical ventilation and detectors needs to be regularly checked at least once a year.
EN 60079–29–2 specifi es in detail the requirements for selection, installation, use and maintenance of detectors of fl ammable gases.
Maintenance Personal Safety Europe
European Union exposure limits for ammonia are defi ned in Directive 2000/39/EC as following:
• TWA 20 ppm / 14mg/m3 • STEL 50 ppm / 35mg/m3
The community limits are set by the European Agency for Safety and Health at Work National limits are defi ned by country regulatory bodies. For example:
UK - Health and Safety Executive - HSE. EH40/2005: • TWA 25 ppm / STEL 35 ppm
France - National Institute of Research and Safety – INRS.
ED 984: • TWA 10 ppm / STEL 20 ppm
Germany - Federal Institute for
Occupational Safety and Health – BAuA. TRGS 900:
• TWA 20 ppm
mmonia was fi rst used as a refrigerant in France, in 1959 by Ferdinand Carré. His invention was a system known as
found in a wide range of HVAC-R applications from occupied spaces such as hospitals, hotels, and public buildings to commercial applications such as cold storage, food processing, ice rinks, and more. The requirements for ammonia gas detection systems are regulated by various standards but
can vary depending on regulations in particular countries. Widely recognised safety standards for ammonia refrigeration systems are: EN 378 Refrigerating systems and heat pumps – Safety and environmental requirements. ISO 5149 Refrigerating systems and heat pumps – Safety and environmental requirements.
ANSI/IIAR 2 Equipment, Design, and Installation of Closed-Circuit Ammonia Mechanical Refrigerating Systems. EN 378 is published in Europe by the European Committee for Standardisation and applies to European Union member states for the majority of refrigeration systems, including commercial refrigeration and stationary air conditioning applications. The standard indicates the requirement for gas detection where the concentration of ammonia in an occupied space may exceed the practical limit which is defi ned at 0,00035 kg/m3 (see Table 1). ISO 5149 is published by the International
Organisation for Standardisation (ISO). It applies to all refrigerating systems where the refrigerant is evaporated and condensed in a closed circuit, including heat pumps and absorption systems. The standard indicates the requirement for gas detection where the concentration of ammonia in an occupied space may exceed the practical limit. It has its equivalent standard in Europe which is EN 378 (see Table 1). ANSI/IIAR 2 is published by the US-based, International Institute of Ammonia Refrigeration (IIAR) and approved by the American National Standards Institute (ANSI). The standard applies to any closed-circuit mechanical refrigerating system using ammonia specifi cally as a refrigerant. It is largely harmonised with ASHRAE Standard 15 – Safety Standard for Refrigeration Systems and captures the industry best practices for using ammonia in industrial applications.
28 December 2023 •
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