Rebreathed Fraction of Air from CO₂

	A	B	C	D	E	G	H	I
1	Rebreathed Fraction of Air					Source:
2	https://tinyurl.com/rebreathed-air-fraction				maintained by: Twitter:@DavidElfstrom
3	420	Co = Outdoor Air CO₂ ppm (note Aranet4 meter calibrates to 420 ppm)
4	38000	Ca = Volume fraction of CO₂ added to exhaled breath (ppm)
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6	Indoor ppm	Fraction	1 in X breaths
7	500	0.2%	475
8	600	0.5%	211
9	700	0.7%	136
10	800	1.0%	100
11	900	1.3%	79
12	1000	1.5%	66
13	1100	1.8%	56			https://doi.org/10.1034/j.1600-0668.2003.00189.x
14	1200	2.1%	49			Risk of indoor airborne infection transmission estimated from carbon dioxide concentration
15	1300	2.3%	43			S. N. Rudnick, D. K. Milton, Indoor Air, Volume 13, Issue 3, September 2003, p237-245
16	1400	2.6%	39
17	1500	2.8%	35
18	1600	3.1%	32			Reasonable approximation
19	1700	3.4%	30			Based on 40,000 ppm in breath and 400 ppm outdoor air:
20	1800	3.6%	28			For every additional 400 ppm over outdoor, rebreathed fraction increases 1%
21	1900	3.9%	26			Indoor CO₂ ppm	Rebreathed	1 in X breaths
22	2000	4.2%	24			400	0%	None
23	2200	4.7%	21			800	1%	100
24	2400	5.2%	19			1200	2%	50
25	2600	5.7%	17			1600	3%	33
26	2800	6.3%	16			2000	4%	25
27	3000	6.8%	15			2400	5%	20
28	3200	7.3%	14			2800	6%	17
29	3400	7.8%	13			3200	7%	14
30	3600	8.4%	12			3600	8%	13
31	3800	8.9%	11			4000	9%	11
32	4000	9.4%	11			4400	10%	10
33	4200	9.9%	10			4800	11%	9
34	4400	10.5%	10			5200	12%	8
35	4600	11.0%	9
36	4800	11.5%	9
37	5000	12.1%	8	⬅ occupational health limit for CO2 exposure (such as for an industrial process using CO2 gas): 5000 ppm, 8-hour time-weighted average
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