Some source said that Freon can be harmful at concentrations higher than 1 part per thousand. The average HVAC has 20 lbs of Freon at most and a 400-sq ft apartment might have 350 lbs of air by my back of the envelope calculation, so in theory this would be a respiratory danger, but at how high a concentration exactly would the Freon or R410 become a suffocation threat?
Sorry, clarification; I’m referring to a Freon-leaking household HVAC.
Freon is (much) heavier than air, so the danger would be a sudden leak displacing a lot of air in a low spot, like a small basement. Inert gas asphyxiation occurs at oxygen concentrations of around 50% of normal (10% instead of the normal 21%,( 6% or less is rapidly fatal)), so the freon would have to displace around 10% of the air volume to be acutely dangerous.
Thanks, but is that 10% applicable to weight as well, I.e., 30 lbs of Freon in a enclosed house with 300 lbs of air, or only volume, I.e., 400 cubic feet of Freon in a 4000 cubic feet of air apartment? I know, of course, that it stays near the ground and that that makes a difference.
I don’t have the standard in front of me, but the Australian standard for refrigerants lists the maximum safe concentration of R410A in an enclosed occupied space as 0.44kg/m3. Not sure what the limiting factor is, but asphyxiation would be a good bet. Typical wall mounted splits have about 2.5kg of refrigerant, somewhere around a 6kW (20,000btuh?) capacity unit, so minimum room volume of 5.6m3 (200ft3). With a ceiling height of 2.4m (8ft) this is a 1.6x1.6m (5x5ft) room. Extremely small for a 6kW unit.
For your example, 20lbs of Freon (I’ll use R410A because I have the numbers) would allow a room volume of 730ft3. For 8ft ceilings, about 90ft2.
All numbers approx as I’m going by memory.
Ok, ‘allow’ as in, not dangerous before this point?
The notes in the standard state that the “practical limit for Group A1 refrigerants is less than half the concentration which can lead to suffocation due to oxygen displacement or which has narcotic or cardias sensitization effects after a short time”. Practical limit as above.
Based on this, I would say the refrigerant is not dangerous in concentrations below this. The listing for the refrigerant does not list LC50 or TWA exposure standard values, so I believe R410A is only displaces oxygen and is non-toxic, whereas Freon (R-12) has a practical limit of 0.5kg/m3, LC50 of 800,000 ppm and a TWA of 1,000 ppm.
The Australian standard is based on BS 4434 and ANSI/ASHRAE 34. Perhaps there is more info in these standards.
NB
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The average HVAC has 20 lbs of Freon at most…
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Well, the average AC unit (in the US, at least) won’t have Freon (R22) at all as it’s been banned for use in new systems since 2010
As for the quantity, 20 pounds of refrigerant would be a HUGE system. A typical 3-ton unit (good for an approximately 1500 square foot house, depending on climate, sun exposure, insulation, ceiling height, etc…) and the lineset that connects the two halves of the system needs about seven pounds of R401a.
The AC for the OP’s hopefully hypothetical apartment is probably only one ton or so, or more likely IME, a pair of 6,000 BTU window/wall units, which combined are approximately equal to one ton of cooling with about 2-3 pounds of refrigerant between the two of them.