RACA Journal May 2026 RACA_May_2026 | Page 41

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proximity of potential ignition sources to installed systems you must risk assess the system to account for: Total refrigerant charge volume, likelihood of leakage, rate of leakage, and other mitigating factors such as exposure to wind which may dissipate any refrigerant leak before the leak reaches the LFL.

For example, if an R290 system is leaking then the leaked refrigerant will not become potentially flammable until the concentration reaches the LFL of 0.038kg / m 3 or approximately 2.1 % by volume. A tiny leak of a few grams a day in a split system outdoor unit, for example, would likely never reach the LFL and therefore not be a fire hazard. A larger leak of the entire refrigerant charge by catastrophic pipe or component failure, however, may present the risk of rapidly reaching the LFL and stay below the UFL of approximately 9.5 % by volume rendering the risk of ignition to be high.

Applying the safety standards to determine maximum refrigerant charge allowable can be complicated, and there really isn’ t an easy answer but with care and planning it is possible to ensure the installations you design or work on are safe for you, your clients and the public.

Calculation for determining the maximum allowable charge of an A2L refrigerant in an air conditioning or heat pump system used for human comfort:

where: mmax is the maximum allowable charge in kg m is the refrigerant charge in the system in kg Amin is the required minimum room area in m 2 A is the room area in m 2 LFL is the lower flammable limit in kg / m 3, taken from the table below ho is the height factor of the appliance:

• 0.6 for floor mounted units

• 1.8 for wall mounted units

• 1 for window mounted units

• 2.2 for ceiling mounted units

Reference: EN378-1:2017-03 Flammability limits

Lower flammability limit( LFL)

Upper flammability limit( UFL)

Auto-ignition temperature

R600a R 290

1.5 % approx. 0.038 kg / m 3 2.1 % approx.

0.038 kg / m 3

8.5 % approx. 0.0203 kg / m 3 9.5 % approx.

0.0171 kg / m 3

460 ° C 470 ° C

Lower and upper flammability limits for R600a and R290

To simplify matters, the above graph illustrates the results when calculated( NOTE: Refer to manufacturers instructions at all times):

• Charges in systems below ground( cellars and basements) are restricted to a maximum of 1.0kg even with larger room sizes. Sealed systems containing a charge of less than 150g can be situated in any location, regardless of room volume.

• Note that all charge limits apply per single refrigerant circuit, on the basis of probability that two circuits will not have catastrophic failures simultaneously.

• Where reasonably practical, charging points for systems shall be in the open air. Where this is not practical they shall not be sited near exit passage ways.

Thank you for the question, Clement. We are moving into a new era with regards to refrigerants and keeping your knowledge and

skills up to date are critical.

grant @ acra. co. za

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