In a city where the technocratic mayor prides himself on making decisions based on the evidence, the proposed ban produced one of the most scientifically vague and emotionally charged health committee hearings in recent memory. Anyone who used the word “smoke” or “smoking” to refer to electronic cigarettes, which typically contain nicotine, was instantly corrected by audience members hissing “Vapor!” and “Vaping!”

The health commissioner, Dr. Thomas A. Farley, said electronic cigarettes were such a recent invention that he could not say whether they were hazardous to the health of those smoking them or those who might breathe in secondhand vapor. He said that they do put out fine particles and chemicals, and “I certainly can’t guarantee that that is safe.”

He said the problem with e-cigarettes was that they made smoking socially acceptable, and that they were a “bridge” for people who went back to smoking regular cigarettes.

“Does it help people quit, or does it help people not quit?” Dr. Farley asked, rhetorically.

Then Dr. Farley indulged in a bit of theater himself, fishing around in his shirt pocket, saying, “Just to give you an idea, I’ve got one here somewhere,” before pulling out an electronic cigarette that he pronounced “indistinguishable” from a real one. He and other supporters of the ban say e-cigarettes confuse people like bartenders and restaurant owners who have to enforce the existing smoking ban, making that ban harder to enforce. Advocates of e-cigarettes argued they had helped many people stop smoking regular cigarettes, including — based on a show of hands — most of the audience. E-cigarettes, which use a battery to vaporize a nicotine solution, have grown in popularity based on a perception that they are a safer smoking alternative.

Dr. Gilbert Ross, executive director of the American Council on Science and Health, which he said received some funding from the e-cigarette industry, told the committee that the proposed law was “hyper-regulatory, and it really will accomplish nothing except to make other former smokers return to toxic cigarettes.”