In the past, refrigerant gases used in home and commercial refrigeration and air conditioning equipment were selected based on their ability to work the most effectively at cooling. As the impact of these gases on climate change were realized, researchers began looking for alternative gases that had the same or similar efficiency - but did not contribute to the greenhouse effect.
Today there are many new refrigerant gases with low environmental impact. However, some of the replacement gases are toxic and flammable. Therefore it is important when using these new gases that refrigerant leak detector sensors be used.
Refrigerant Gas History
Early refrigerants were often flammable and toxic. Throughout the 1800s gases like petrol ether, sulfur dioxide, ammonia and methyl chloride were used. Many of these gases were reactive, resulting in leaks and explosions due to equipment failure or improper handling. They also tended to be toxic, at one point resulting in people leaving their refrigerators in their back yards.
In 1928 Thomas Midgley, Jr. invented Freon, a gas composed of chlorofluorocarbons (CFCs) that was both non-reactive and non-toxic. Because it eliminated the danger posed by leaks, CFCs became the most widely used refrigerant gas in the world.
Commercial CFC production began in the 1930’s with R-12, R-11, R-114 and R-113. R-22 hydrofluorocarbons (HFCs) were produced in 1936. By 1963 CFCs and HFCs accounted for 98% of total production of fluorine gases.
Today, CFCs and Freon are recognized as a major contributor to the depletion of the Earth’s ozone shield. As a result, most CFCs are banned or severely restricted worldwide. In addition, Freon containing HFCs are also under strict worldwide control due to their contributing to the “greenhouse effect."
Modern Refrigerant Gases
While modern Hydrocarbon and HFO (hydro fluoro olefin) refrigerant gases no longer pollute the way CFCs and HFCs do, many of them are slightly toxic and flammable. They are rated 1-3 according to flammability and A or B according to their level of toxicity as follows:
|
|
Lower Toxicity |
Higher Toxicity |
|
Higher Flammability |
A3 |
B3 |
|
Lower Flammability |
A2 / A2L |
B2 / B2L |
|
No Flammability |
A1 |
B1 |
For example, lower flammability (A2L) refrigerant gases include R-32, R-454 blends and R-1234yf. The gases R-134A, R-407C, R-404A and R-410A are all commonly used in HVAC applications.
In addition to toxicity and flammability, each refrigerant gas is rated according to its ozone depletion potential (ODP) and global warming potential (GWP). Information on all refrigerant gases are listed on their material data safety sheets. This information has been codified by the U.S. Environmental Protection Agency in the Final Rule - Phasedown of Hydrofluorocarbons: Establishing the Allowance Allocation and Trading Program under the AIM Act.
While only a few refrigerant gases make up the bulk of all refrigerant gases sold, their are over a hundred different types available on the market. For a list of all the refrigerant gases, ASHRAE has a comprehensive list of refrigerant gas Designation numbers with their chemical composition. Wikipedia also has a comprehensive list that includes the gas type as well as their ODP and GWP ratings.
Testing for Flammability
Comparisons of flammability of gases use the lower flammable limit measurement. LFL is the smallest concentration of a gas as a percent by volume that will produce a flash or flame.
- Class 1 refrigerants are either non-combustible, or do not support the spread of a flame in a combustible environment.
- Class 2 refrigerants have a lower flammability limit of more than 0.00624 lb./cubic foot (0.10kg/cubic meter) at 70 degrees F and 14.6 psi, and a heat of combustion less than 19 kilojoules/kilogram.
- Class 3 refrigerants are highly flammable with a lower flammability limit of less than or equal to 0.00624 lb./cubic foot (0.10 kg/cubic meter) at 14.6 psi and 70 degrees F, or a heat of combustion greater than or equal to 19 kilojoules/kilogram.
All flammable refrigerants (class 2L and above) will not ignite if the concentration level in a room stays below their lower flammability limit (LFL).
CO2 as a Refrigerant Gas
Over the past decade, R744 CO2 refrigerant systems have gained growing acceptance as an alternative to traditional HCFC (hydro-chlorofluorocarbon) type R22 refrigerant or ammonia-based systems in the food and food transportation industries. For example, the Dollard-des-Ormeaux Civic Centre in Quebec, Canada now uses a carbon dioxide refrigeration system to freeze the floor of the ice rinks as well as provide building heating.
Primary drivers for the increased use of CO2-based refrigeration systems include improved safety by eliminating the use of ammonia and lower life-time operating costs. R744 CO2 gas is rated as A1, which is not flammable.
Limitations to use include legislation, regulations, higher initial system costs, and contractor and end-user training.
Ammonia as a Refrigerant Gas
Modern grocery stores are switching from R717 ammonia (NH3) gas to newer R-32 gases or CO2 to keep their meat, dairy and frozen food isles cold. Ammonia is classified as a Group B2L refrigerant because of toxicity and flammability concerns.
Refrigerant Gas Sensors
Refrigeration and air cooling equipment is ever-present in our lives. From our home HVAC system to cars to where we work and shop: everywhere we go presents a potential exposure to flammable refrigerant gas leaks.
To protect against possible leaks, the ASHRAE Standard 15 was developed. This standard details when a refrigerant monitor is necessary. Standard 15 also details that an alarm must have visible and audible cues to alert an operator of a leak.
Refrigerant gas monitors that meet these specifications like the Nevada Nano MPS Refrigerant Gas Sensor or the Cubic R32 A2L Refrigerant Sensor are both designed to be incorporated into gas leak detection and mitigation systems.
For CO2-based refrigerant systems, there are many dependable and low-cost CO2 sensors that can be used for leak detection. For example,
References
Merry, Michael. "What Refrigerants Are Flammable?" https://sciencing.com/refrigerants-flammable-8573450.html
ANSI/ASHRAE 15-2016 Addendum A. https://www.ashrae.org/file%20library/technical%20resources/standards%20and%20guidelines/standards%20addenda/15_2016_a_20180628.pdf
ANSI/ASHRAE 34-2019. Designation and Safety Classification of Refrigerants.
UL 60335-2-40 Refrigerant Detector Requirements. https://www.ul.com/news/understanding-ul-60335-2-40-refrigerant-detector-requirements
Lower Flammable limit, Wikipedia. https://en.wikipedia.org/wiki/Lower_flammable_limit
EPA. “Refrigerant Safety” https://www.epa.gov/snap/refrigerant-safety