Because ETS contains Carbon Monoxide, and virtually any prolonged exposure to Carbon Monoxide over the zero baseline level is a health hazard. You may want to take that up with OSHA and the EPA. Those agencies have established criteria other than "virtually any exposure over the zero baseline level."
Carbon Monoxide (CO) Response <-- Link
"The Occupational Safety and Health Administration (OSHA) has established a maximum safe working level for carbon monoxide at 35 parts per million (ppm) over an 8 hour period, in the general work-place. The U.S. Environmental Protection Agency (EPA) has established that residential levels are not to exceed 9 ppm over an 8 hour average."
IMO, the safe level is somethng other than zero, even for continuous exposure.
" You may want to take that up with OSHA and the EPA. Those agencies have established criteria other than "virtually any exposure over the zero baseline level."
Carbon Monoxide (CO) Response <-- Link
"The Occupational Safety and Health Administration (OSHA) has established a maximum safe working level for carbon monoxide at 35 parts per million (ppm) over an 8 hour period, in the general work-place. The U.S. Environmental Protection Agency (EPA) has established that residential levels are not to exceed 9 ppm over an 8 hour average."
The last time I looked at a CO detector the minimum detectable of amount of CO was 9 PPM. Thanks for proving my point.