Table 5.

Cancer risk (LTCR) related to formaldehyde concentrations in indoor and outdoor air of waterpipe cafés.

Cafés			Average	Min	Max	I/O ratio
						Week-day	Weekend
Waterpipe	Indoor	Week-day	111 × 10−5	25.1 × 10−5	194 × 10−5	7.15	3.94
		Weekend	61.2 × 10−5	36.6 × 10−5	232 × 10−5
	Outdoor	Week-day	15.3 × 10−5	—	39.6 × 10−5
		Weekend	15.5 × 10−5	—	30.4 × 10−5
Cigarette	Indoor	Week-day	33.7 × 10−5	240 × 10−5	47.9 × 10−5	3.09	4.52
		Weekend	39.4 × 10−5	27.4 × 10−5	50.7 × 10−5
	Outdoor	Week-day	10.9 × 10−5	—	24.4 × 10−5
		Weekend	8.70 × 10−5	—	27.3 × 10−5
Waterpipe and cigarette	Indoor	Week-day	271 × 10−5	224 × 10−5	345 × 10−5	14.6	18.4
		Weekend	322 × 10−5	249 × 10−5	416 × 10−5
	Outdoor	Week-day	18.5 × 10−5	5.10 × 10−5	291 × 10−5
		Weekend	17.5 × 10−5	—	39.2 × 10−5
Non-smoking	Indoor	Week-day	4.80 × 10−5	—	11.5 × 10−5	0.470	0.590
		Weekend	5.90 × 10−5	—	19.4 × 10−5
	Outdoor	Week-day	10.1 × 10−5	—	43.4 × 10−5
		Weekend	9.90 × 10−5	—	37.0 × 10−5