- Explain the ASHRAE 34 safety classification system for refrigerants (A1, A2L, A2, A3)
- Define lower flammability limit (LFL) and burning velocity for A2L refrigerants
- Compare A2L ignition characteristics to A1 (non-flammable) and A3 (highly flammable) refrigerants
- Identify which common low-GWP refrigerants carry the A2L classification
Leçon 1
The ASHRAE 34 Safety Classification System
Two-Part Safety Rating
Every refrigerant receives a safety classification under ASHRAE Standard 34, which has been adopted by reference in building codes and equipment safety standards worldwide. The classification uses a letter-number system where the letter indicates toxicity and the number indicates flammability.
Toxicity classes:
- A = Lower toxicity (occupational exposure limit above 400 ppm)
- B = Higher toxicity (occupational exposure limit at or below 400 ppm)
Flammability classes:
- 1 = No flame propagation (non-flammable)
- 2L = Lower flammability with low burning velocity (mildly flammable)
- 2 = Lower flammability (flammable)
- 3 = Higher flammability (highly flammable)
The "2L" subclass was created specifically for the new generation of low-GWP refrigerants that are technically flammable but burn so slowly that they present a much lower fire risk than Class 2 or Class 3 refrigerants.
A1 - Non-Flammable
Refrigerants: R-410A, R-134a, R-404A
Flammability: Will not ignite under test conditions
Special tools: Not required
Charge limits: None based on flammability
A2L - Mildly Flammable
Refrigerants: R-32, R-454B, R-1234yf, R-1234ze
Flammability: Burns slowly, hard to ignite
Special tools: Spark-proof in some applications
Charge limits: Based on room size and LFL
A3 - Highly Flammable
Refrigerants: R-290 (propane), R-600a (isobutane)
Flammability: Ignites easily, burns rapidly
Special tools: Required - spark-proof everything
Charge limits: Strict - 150g maximum for commercial equipment
Why A2L Is a Distinct Category
The "L" in A2L stands for "lower burning velocity." A2L refrigerants have a maximum burning velocity of less than 10 cm/s (centimeters per second). For comparison, propane (A3) has a burning velocity of approximately 40 cm/s, and natural gas burns at about 38 cm/s. The slow burning velocity of A2L refrigerants means:
- Flames propagate slowly and are easily extinguished by air movement
- The refrigerant requires a stronger ignition source to ignite
- Fire spread is significantly slower than with traditional flammable gases
ASHRAE 34 classifies refrigerants by toxicity (A/B) and flammability (1/2L/2/3). A2L refrigerants like R-32 and R-454B burn at less than 10 cm/s - roughly one-quarter the speed of propane. This slow burn rate is why A2L requires fewer safety precautions than A3 while still demanding more care than A1.