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Tech Talk - Part 3

Refrigerant Safety
Designations
A1 to B3

PART 3

NON-TOXIC
The definition of "safety" is "being free from harm or the risk of injury or loss." The concerns usually associated with refrigerant safety are toxicity, flammability, and physical hazards.

The responsibility of finding a nontoxic/nonflammable refrigerant with good stability was given to Thomas Midgley in 1928. Midgley was already a success by finding tetraethyl lead, to improve the octane rating of gasoline. He secretly suffered from lead poisoning because of his invention, a fact he kept hidden from the public.

Midgley and his associates Albert L. Henne and Robert R. McNary observed that the refrigerants used were of relatively few chemical elements. They eliminated those with insufficient volatility, and then eliminated those that resulted in unstable and toxic compounds as well as the inert gases, based on their low boiling points. Left with just eight elements: carbon, nitrogen, oxygen, sulfur, hydrogen, fluorine, chlorine, and bromine, Midgley noted they clustered at an intersecting row and column of the periodic table of the elements, with fluorine at the intersection. These three points became apparent. flammability decreases from left to right for the eight elements
toxicity generally decreases from the heavy elements at the bottom to the lighter elements at the top
All known refrigerants at the time were made from combinations of those elements.
Two mistakes or errors that occurred during the search actually helped in the development. During their search, their attention to organic fluorides was caused by an error in the literature. It showed the boiling point for tetrafluoromethane (carbon tetrafluoride) to be high compared to those for other fluorinated compounds. The correct boiling temperature was later found to be much lower. But the incorrect value was in the range sought. This led them to evaluating organic fluorides as candidates.

Then in performing the first toxicity test, Midgley exposed a guinea pig to the new compound. The animal was completely unaffected, but when the test was repeated with another sample, the animal died. This led to the examination of the process used to prepare the dichlorodifluoromethane from carbon tetrachloride. It showed that four of the five sampling bottles available at the time contained water. This contaminant had formed phosgene (COCl2) during the reaction process with carbon tetrachloride. Think about it. If Midgley had used one of the other samples in the initial test, the discovery of organic fluoride refrigerants may have been delayed for years.

To demonstrate the physical properties of the refrigerant, for the American Chemical Society in 1930, Midgley inhaled a lung-full of the new wonder gas, exhaled onto a candle flame and extinguished it, showing the gas's non-toxicity and non-flammable properties. While dramatic, this demonstration was violation of today’s safe handling practices.

Frigidaire was issued the first patent, US#1,886,339, for the formula for CFCs on December 31, 1928. In 1930, General Motors and DuPont formed the Kinetic Chemical Company to produce Freon. By 1935, Frigidaire and its competitors had sold 8 million new refrigerators in the United States using Freon made by the Kinetic Chemical Company.

PAFT Tests
The Program for Alternative Fluorocarbon Toxicity Testing (PAFT) is a cooperative effort sponsored by the major producers of CFCs from nine countries. PAFT was designed to accelerate the development of toxicology data for fluorocarbon substitutes, as refrigerants and for other purposes. Examples of the other uses include as blowing agents, aerosol propellants, and solvents. The PAFT research entails more than 100 individual toxicology tests by more than a dozen laboratories in Europe, Japan, and the United States. The first tests were launched in 1987, to address R-123 and R-134a (PAFT I). Subsequent programs were initiated for R-141b (PAFT II), R-124 and R-125 (PAFT III), R-225ca and R-225cb (PAFT IV), and R-32 (PAFT V). The cost of testing for each compound is $1-5 million and the duration is 2-6 years, depending on the specific tests deemed necessary or indicated by initial findings.

These PAFT studies investigate acute toxicity (short-term exposures to high concentrations, such as from accidental releases), subchronic toxicity (repeated exposure to determine any overall toxicological effect), and chronic toxicity and carcinogicity (lifetime testing to assess late-in-life toxicity or potential to cause cancer). The experiments also gauge genotoxicity (effects on genetic material, an early screen for possible cancer-inducing activity), reproductive and developmental toxicity (teratology, assessment of the effects on the reproductive system and of the potential for causing birth defects), and ecotoxicity (assessment of potential to affect living organisms in the environment).

Short term exposures at high concentrations indicate any acute hazards such as irritation, sensitization of the heart or adrenaline and lethal concentration (LC50 is the amount which kills half the animals in a short amount of time).
Tests that expose animals for longer periods of time, such as 90 days to two years, are designed to indicate chronic problems. These can include mutagenicity (changes to cells), reproductive problems, and effects on organs or carcinogenicity (cancer-causing).

A new program, initiated in 1994, is addressing the mechanistic causes of tumors and other effects observed in other programs. PAFT M was spurred by findings of benign tumors in earlier tests of R-123, R-134a, and R-141b. Although the tumors occurred late in life and were neither cancerous nor life threatening, a better understanding of causal effects is being sought.

All substances are poisons in sufficient amounts. For example, toxic effects have been observed for such common substances as water, table salt, oxygen and carbon dioxide in extreme quantities. The difference between those substances regarded as safe and those viewed as toxic is the quantity or concentration needed to cause harm and, in some cases, the duration or repetition of exposures. Substances that pose high risks with small quantities, even with short exposures, are regarded as highly toxic. Those for which practical exposures cause no harm are viewed as safer.

ASHRAE Standard 34* provides a safety classification for refrigerants based on information related to personal exposure. ASHRAE Standard 15** uses this safety rating and additional toxicity information to set requirements for machinery rooms and sets limits on the amount of refrigerant allowed in systems outside machinery rooms. Many blends containing these individual components are also classified.

Refrigerants not classified in ASHRAE Standard 34 should be reviewed with suppliers to make sure enough is known about their toxicity properties. Some blends may not be classified, but contain classified components. (Note: Many building codes have adopted the newer refrigerants listed in ASHRAE standards. Some building codes have not, and therefore, require special permits. A refrigerant that's not listed most likely will require an engineering study to determine if it can be used safely.)

Standard 34 - Class A signifies refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm by volume, based on data used to determine Threshold Limit Value–Time-Weighted Average (TLV–TWA) or consistent indices.
Class B signifies refrigerants for which there is evidence of toxicity at concentrations below 400 ppm by volume, based on data used to determine TLVTWA or consistent indices.

Exposure levels are values given to refrigerants to indicate how much of the chemical a person can regularly be exposed to without adverse effects. All toxicity test results are considered when setting this level. The American Conference of Government and Industrial Hygienists (ACGIH) set the TLV-TWA values for chemicals. The maximum value for any chemical is 1,000 ppm, though many refrigerants have shown no effects in toxicity testing at values much higher than that. Other organizations and chemical producers have similar exposure level indexes based on the same criteria. These are the Workplace Environmental Exposure Limit (WEEL) set by the American Industrial Hygiene Association (AIHA); Permissible Exposure Limit (PEL) set by OSHA; and Acceptable Exposure Limit (AEL) used by DuPont.

There are also the Short Term Exposure Limit (STEL), which is based on a 15-minute exposure time in any given day as well as the value Immediately Dangerous to Life or Health (IDLH). These are used to give guidance for machinery room requirements, ventilation and alarms in an emergency or escape situation or in circumstances where short releases of refrigerant are expected, which could include refrigerant transfers or servicing large equipment.

Toxicity data is usually summarized in great detail on Material Safety Data Sheets (MSDS). What all of this data means to the technician, however, is that commercial refrigerants are safe enough to use provided you don't breathe too much of them. Industry practices for handling refrigerant are intended to minimize personal exposure as well as reduce releases into the atmosphere.

General rules to follow are:
Minimize the amount of refrigerant released. Proper recovery procedures, including clearing hoses, will keep the refrigerant in the containers instead of potentially exposing it to people.
Never intentionally release refrigerant in a confined space. Even the safest refrigerant can still displace enough oxygen to cause suffocation.
Set up ventilation equipment, like a portable fan, in areas where possible release would mean high concentrations.
Refer to ASHRAE Standard 15 and local building codes for additional guidance.

If someone is exposed to refrigerant get him to fresh air, give oxygen if needed, and get him checked by a doctor.

From the PAFT studies and as published on the EPA web site:

Tests of R-123 indicate that it has very low acute inhalation toxicity, as measured by the concentration that causes 50% mortality in experimental animals, a 4-hour LC50 of 32,000 ppm in rats. A cardiac sensitization response was observed at approximately 20,000 ppm. This response was measured in experimental screening with dogs, with simultaneous injection of epinephrine to simulate human stress reactions. Anesthetic-like effects (e.g., weakness, disorientation, or incoordination) were observed at concentrations greater than 5,000 ppm, or 0.5%. R-123 has very low dermal toxicity (by skin application) and is only a mild eye irritant. Long-term inhalation caused an increase in the incidence of benign tumors in the liver, pancreas, and testis of rats. None of the tumors attributable to the exposures were malignant or life-threatening; all occurred near the end of the study, late in the lives of the test specimens. The exposed animals actually exhibited higher survival rates at the end of testing than those in the control group. The rats exposed to higher concentrations also experienced slight reductions in body weight and decreases in cholesterol and triglyceride levels. Studies are continuing to investigate the biological relevance of the tumors to humans. The tests completed to date indicate that R-123 is neither a developmental toxicant nor a genotoxin.

Based on the findings of extensive testing, R-123 has been deemed to have low toxicity. Refrigerant manufacturers recommend that long-term, occupational exposures not exceed limits of 10 and 30 ppm, on eight-hour time-weighted average (TWA) bases. One manufacturer suggests a limit of 100 ppm, also TWA, but is expected to revise this recommendation to somewhere in the 10-30 ppm range. The differences in recommended limits stem from conservative interpretation of the data. As discussed below, occupational exposures can be held well below even the most stringent of these recommendations.
R-134a also has very low acute inhalation toxicity. The lowest concentration that causes mortality in rats, the 4-hour Approximate Lethal Concentration (ALC), exceeds 500,000 ppm. The cardiac sensitization response level for R-134a is approximately 75,000 ppm. Anesthetic-like effects are observed at concentrations greater than 200,000 ppm, or 20%. Long term exposures with very high concentrations, 50,000 ppm, caused an increased incidence of benign tumors in the testis of rats. Again, none of the observed tumors were life-threatening, and all occurred near the end of the study. The evidence from all tests in cultured cells or organisms, as well as in laboratory animals, indicates that R-134a in not genotoxic and that the increased incidence in benign tumors is not due to an effect on genetic material.

The test findings indicate that R-134a has very low acute and subchronic inhalation toxicity, is not a developmental toxicant, and is not genotoxic. Most refrigerant manufacturers recommend that TWA occupational exposures not exceed 1,000 ppm; this also is the level recommended by the American Industrial Hygiene Association, Workplace Environmental Exposure Limit (WEEL) Committee. Again, exposures still should be kept to the practicable minimum.

It is important to note that the tumors attributable to the R-123 and R-134a exposures were not cancerous. The findings reflect an increase in tumor incidence compared to rats in the experimental control group, those not exposed to the refrigerants. Some tumors also were observed in this control group, but not as many. Also, the recommended occupational exposure limits for each refrigerant is below the level at which toxic effects were observed in laboratory animals. The use of rats, dogs, and other animals is based on accepted scientific procedures and sensitivities to specific concerns by species. The lower exposure limit affords both a margin of safety and a conservative reflection of potential differences, between responses in individual humans and between humans and test animals.

The exposure limits for refrigerants are based on chronic toxicity concerns and are below those at which toxic effects were observed in the laboratory tests. Higher concentrations are allowable for short-periods, but exposures still should be kept to a practical minimum, as for all chemicals.

Flammability/Combustion/Decomposition

Flammable refrigerants present an immediate danger when released into the air. The refrigerant can combine with air at atmospheric pressure and ignite, causing a flame and possibly an explosion to occur. Because of the obvious hazards, the use of flammable refrigerants is restricted to controlled environments that have monitors, proper ventilation, explosion-proof equipment and generally few people near the equipment (refineries, storage warehouses, breweries, etc.).

Some refrigerants can burn with oxygen, but only at higher pressures or temperatures and never in air at atmospheric conditions. These are called "combustible" refrigerants. Underwriter's Laboratories (UL) lists these refrigerants as "Practically Nonflammable."
R-22 and R-134a fall into this category. R-22 was found to cause a combustion hazard during a pressurized leak test with air. For this reason, most refrigerants should be used only with pressurized nitrogen for leak testing. As long as refrigerant is not pressurized with large amounts of air, there should be little hazard from these refrigerants during normal handling and use.

So how is a refrigerant determined to be non-flammable at atmospheric conditions?

ASTM E 681 – 04

Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases) - This test method covers the determination of the lower and upper concentration limits of flammability of chemicals having sufficient vapor pressure to form flammable mixtures in air at atmospheric pressure at the test temperature. This test method may be used to determine these limits in the presence of inert dilution gases. No oxidant stronger than air should be used. The standard specifies the testing apparatus and test conditions.
ASHRAE 34 - 8.7.1 Flame Propagation. Applications for single-compound refrigerants and for refrigerant blends shall include test results determined in accordance with E681. Applications shall include a description of the apparatus and methods used,
including (but not limited to)

schematic of the apparatus,
vessel size and shape,
ignition method,
preparation procedures including cleaning between
tests,
method(s) used to control and verify test concentration(s),
how horizontal flame propagation was determined.
8.7.2 Fractionation Analysis. Applications shall include an analysis of fractionation.

A 2.5-liter cylinder was cleaned and evacuated prior to use. The cylinder was then filled with the WCF of the blend to the required 15% of the maximum DOT fill volume for the blend. The volume of the liquid in the cylinder was calculated using the liquid density of the refrigerant at the ambient temperature. The cylinder was then completely immersed in an appropriate bath at the specified temperature for one hour. The initial liquid and vapor samples were taken and analyzed (see GC procedure).
While the cylinder was still immersed in the appropriate temperature bath (+10* NBP), the vapor phase of the cylinder was purged at a rate of 2% or less of the initial weight per hour. After the purging period, the vapor and liquid phases of the refrigerant were sampled for composition. Measurements were taken at 2% intervals for the first 10% and then at 10% intervals until no liquid phase remained.

Decomposition can occur with any refrigerant when it gets hot enough. Refrigerant can decompose in systems or containers exposed to fire or other extreme heat, electrical shorts (burnouts), or in refrigerant lines being soldered or brazed without being cleared first. Obviously, refrigerant containers or charged systems should never intentionally be exposed to a flame or torch.

When a refrigerant is decomposed or burned, the primary products formed are acids: Hydrochloric acid (HCI), if the refrigerant contains chlorine, and hydrofluoric acid (HF), if it contains fluorine. These products are formed when hydrogen is present, such as from the breakdown of oil, water or if the refrigerant has hydrogen attached (like R-22 or R-134a). If oxygen also is present (from air or water), then it's possible to form carbon monoxide, carbon dioxide and various unsaturated carbonyl compounds – such as phosgene.
Since phosgene is extremely toxic in small amounts, the formation of it was a real concern when refrigerants (R11, R-12, R-113, R-114) decomposed. Phosgene contains two chlorine atoms and an oxygen atom. It will only form when oxygen is present and only the refrigerants with chlorine attached will produce phosgene (not HFCs). R22 only has one chlorine atom per molecule, so chemically speaking it is extremely difficult to get another one attached to form phosgene. Decomposition of R-22 or HFCs may form other carbonyl fluorides; however they are not as toxic as phosgene.

· Thévenot, R. 1979. A History of Refrigeration Throughout the World. Translated from French by J.C. Fidler. Paris, France: International Institute of Refrigeration (11R).
· Downing, R. 1966. "History of the organic fluorine industry." Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed. New York, New York: John Wiley and Sons Inc. Vol. 9, pp. 704-707.
· Nagengast, B. 1989. "A history of refrigerants." CFCs: Time of Transition, Atlanta, Georgia: ASHRAE, pp. 3-15.
· Midgley, T. 1937. "From the periodic table to production." Industrial and Engineering Chemistry. Vol. 29, pp. 239-244.
· Midgley, T., Henne, A. 1930. "Organic fluorides as refrigerants." Industrial and Engineering Chemistry. Vol. 22, pp. 542-547.
· Downing, R. 1988. Fluorocarbon Refrigerants Handbook. Englewood Cliffs, New Jersey: Prentice Hall.
· Klaassen, C., et al. 1991. Casarett and Doull's Toxicology - The Basic Science of Poisons. New York, New York: Pergamon Press.
· Brock, W. 1993. "When is a substance really safe?" Air-Conditioning, Heating, and Refrigeration News. Troy, Michigan: Business News Publishing Co. October 11.

· Finegan, C., Rusch, G. 1993. "Update: Program for alternative fluorocarbon toxicity testing." Stratospheric Ozone Protection for the 90's (Proceedings of the International CFC and Halon Alternatives Conference.) Arlington, Virginia: Alliance for Responsible CFC Policy. October, pp. 895-904.
· PAFT, 1993. PAFT Toxicology Summaries. Bristol, United Kingdom: Program for Alternative Fluorocarbon Toxicity Testing. September.
· AIHA. 1991. Workplace Environmental Exposure Level Guide: 1,1,1,2-tetrafluoroethane. Fairfax, Virginia: American Industrial Hygiene Association.
· ARTI. Toxicity of Refrigerants. Arlington, Virginia: Air-Conditioning and Refrigeration Technology Institute. Project 660-50001, completion anticipated in 1995.
· ASHRAE. 1992. ANSI/ASHRAE Standard 34-1992, Number Designation and Safety Classification of Refrigerants. Atlanta, Georgia: ASHRAE.
· Pillis, J. 1994. "Expanding ammonia usage in air conditioning." R-22 and R-502 Alternatives (Proceedings of the ASHRAE/NIST Refrigerants Conference). Gaithersburg, Maryland, pp. 103-107.
· EPA. 1994. "Protection of stratospheric ozone, final rule amending 40 CFR Parts 9 and 12." Federal Register. Washington, DC: US Environmental Protection Agency, pp. 13044- 13161, March 18.
· Checket-Hanks, B. 1991. "R-22 leak at ice rink kills one, injures 34." Air-Conditioning, Heating, and Refrigeration News. Troy, Michigan: Business News Publishing Co. May 27, pp. 1-2.
· ASHRAE. 1992. ASHRAE Standard 15-1992, Safety Code for Mechanical Refrigeration. Atlanta, Georgia: ASHRAE.
· Sand, J., Andrejeski, D. 1982. "Combustibility of chlorodifluoromethane." ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 24, No. 5, May, pp. 38-40.
· Dekleva, T., et al. 1993. "Flammability and reactivity of select HFCs and mixtures." ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 35, No. 12, December, pp. 40, 42, 44-47.
· ARI. 1994. ARI Flammability Workshop. Arlington, Virginia: Air-Conditioning and Refrigeration Institute. March.
· Meridian Research Inc. 1991. Results of Employee Exposure Monitoring for HCFC-123 at Centrifugal Chiller Installations. Washington, DC: US Environmental Protection Agency. November 26.
· Trane. 1991. Report on Testing and Analysis of the Concentration of HCFC-123 in Field Installations with General Machinery Rooms Containing Hermetic Centrifugal Chillers. Report CFC-1. La Crosse, Wisconsin: Trane, October.

· Trane. 1992. Report of Worker Exposure to HCFC-123 During Servicing of Hermetic Centrifugal Chillers. Report CFC- 2. La Crosse, Wisconsin: Trane. May.
· ACGIH. 1992. 1992-1993 Threshold Limit Values for Chemical Substances in the Work Environment, 1992-1993 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, Ohio: The American Conference of Government Industrial Hygienists. p. 5.
· Sibley, H. 1992. A Study for Determining Refrigerant Exposure Levels while Servicing an HCFC-123 Centrifugal Chiller. Report 819-061. Syracuse, New York: Carrier Corp. April.
· DuPont. 1992. Suva 123 (Suva Centri-LP, HCFC-123) in Chillers. Report ART-2 (H-42443). Wilmington, Delaware: DuPont Chemicals.
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· Burgett, L. "Revised standards for mechanical refrigeration." ASHRAE Journal, Atlanta, Georgia: ASHRAE. Vol. 35, No. 8, August, pp. 31-35.
· ASHRAE. 1993. ANSI/ASHRAE Standard 34a-1993, Addendum to Number Designation and Safety Classification of Refrigerants. Atlanta, Georgia: ASHRAE. August.
· ASME. 1992. "Rules for construction of pressure vessels." ASME Boiler and Pressure Vessel Code. New York, New York: American Society of Mechanical Engineers. Section VIII, Division 1.
· Richard, R., Shankland, I. 1992. "Flammability of alternative refrigerants." ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 34, No. 4, April, pp. 20, 22-24.
· ECETOC. 1989. Chlorodifluoromethane - CAS: 75-45-6. Joint Assessment of Commodity Chemicals (JACC) report 9. Brussels, Belgium: European Chemical Industry Ecology and Toxicology Centre. October 19.
· ECETOC. 1990. 1,1-dichloro-2,2,2-trifluoromethane [2,2- dichloro-1,1,1-trifluoromethane] (HFA-123) - CAS Registry Number 306-83-2. JACC report 13. Brussels, Belgium: European Chemical Industry Ecology and Toxicology Centre. May.
· NIOSH. Registry of Toxic Effects of Chemical Substances (RTECS). Online database. Washington, DC: National Institute for Occupational Safety and Health, US Department of Health and Human Services.
· Calm, J., et al. 1993. Refrigerant Safety Data - Recommendations of the Air-Conditioning and Refrigeration Industry. Arlington, Virginia: Air-Conditioning and Refrigeration Institute. October.
· Syracuse Research Corp. 1990. Toxicological Profile for Ammonia. Report TP-90-0. Washington, DC: US Department of Health and Human Services. December.
Nagengast, B. 1991. “John Gorrie, pioneer of cooling and icemaking.” ASHRAE Journal (33) 1:S60

Archive Articles
- Talking the Talk and Walking the Walk
- Tech Talk - Part 1
- Tech Talk - Part 2
- Tech Talk - Part 3
- Tech Talk Hydrocarboncomp