3.2 Refrigerant Classification, ASHRAE Numbering, and Safety Groups

Every refrigerant on the EPA 608 exam belongs to a chemical family and carries an ASHRAE safety classification. These two systems answer different questions: the chemical family tells you how the refrigerant affects the atmosphere and when it is being phased out, while the ASHRAE safety group tells you how dangerous it is to handle. Knowing both — and how to read an R-number — lets you reason about any refrigerant you encounter, even unfamiliar ones.

The Five Chemical Families

The single most important variable across these families is chlorine. Chlorine is what destroys ozone, so the industry has moved progressively from chlorine-heavy CFCs toward chlorine-free naturals and HFOs.

CFCs — Chlorofluorocarbons (Class I ODS)

• Contain chlorine, fluorine, and carbon — no hydrogen.
• Highest ODP and extremely stable, persisting 50-100+ years in the atmosphere.
• Production banned in developed countries since 1996.
• Examples: R-11, R-12, R-113, R-114, R-502.

HCFCs — Hydrochlorofluorocarbons (Class II ODS)

• Contain hydrogen, chlorine, fluorine, and carbon.
• Lower ODP than CFCs — the hydrogen makes them less stable so they degrade faster.
• R-22 production ended January 1, 2020; full HCFC phaseout by 2030.
• Examples: R-22, R-123, R-124, R-141b.

HFCs — Hydrofluorocarbons

• Contain hydrogen, fluorine, and carbon — no chlorine.
• Zero ODP but often high GWP.
• Subject to the AIM Act HFC phasedown.
• Examples: R-134a, R-404A, R-407C, R-410A, R-32.

HFOs — Hydrofluoroolefins

• Like HFCs but with a carbon-to-carbon double bond, which makes them break down quickly in the lower atmosphere.
• Zero ODP and very low GWP (often below 10).
• The newest synthetic generation.
• Examples: R-1234yf, R-1234ze.

Natural Refrigerants

• Naturally occurring substances: R-717 (ammonia), R-744 (CO2), R-290 (propane), R-600a (isobutane).
• Zero ODP and generally very low GWP.

ODS Classification: Class I vs. Class II

EPA divides ozone-depleting substances (ODS) into two regulatory classes.

A frequent exam point: HFCs are not ozone-depleting substances and appear in neither class — they are regulated separately under the AIM Act for their climate impact.

ASHRAE Standard 34 Safety Classification

ASHRAE Standard 34 assigns every refrigerant a two-character safety group. The letter rates toxicity and the number rates flammability.

Letter — toxicity (based on the occupational exposure limit, OEL):

• A = lower toxicity (OEL ≥ 400 ppm)
• B = higher toxicity (OEL < 400 ppm)

Number — flammability:

• 1 = no flame propagation
• 2L = lower flammability (burning velocity ≤ 10 cm/s)
• 2 = flammable
• 3 = higher flammability

The 2L subclass matters enormously for 2026 service work because the industry is shifting from A1 refrigerants to mildly flammable A2L refrigerants like R-454B and R-32 in new equipment.

Reading the R-Number

The R-number encodes the molecule for single-component refrigerants (methane and ethane series):

• Hundreds digit = (number of carbon atoms) − 1
• Tens digit = (number of hydrogen atoms) + 1
• Units digit = number of fluorine atoms

For blends and naturals, the series tells you the type:

Worked Example: Decode R-134a. Hundreds digit = 1, so carbons = 1 + 1 = 2. Tens digit = 3, so hydrogens = 3 − 1 = 2. Units digit = 4, so fluorines = 4. The molecule is therefore C2H2F4 (tetrafluoroethane), and the trailing "a" denotes the specific isomer. Because it contains no chlorine, its ODP is 0 — exactly what the family classification (HFC) already told you. This cross-check, reading both the number and the family, is the kind of reasoning the Core section rewards.

When a new refrigerant appears, classify it in two passes: first the chemistry (does it contain chlorine? → ODP and phaseout), then the ASHRAE group (how toxic, how flammable? → handling precautions). That two-pass habit will carry you through any classification question on the exam.