Parents who smoke in their cars would no longer be able to light up if they have small children strapped in under a bill that was approved Monday by the Senate.

Debate over the measure, which passed second reading 20-9, has come down to lawmakers weighing the rights of an adult smoker in a private, unregulated space with the rights of children age 5 and under not to breathe the resulting secondhand cigarette smoke.

Concerns about private property rights were offset by the fact that the infraction is only secondary, the $45 fine is waived if the driver enrolls in a smoking-cessation class, and the citation cannot be used in a child-neglect or abuse investigation.

The bill's sponsor, Sen. Scott McCoy, D-Salt Lake, said the measure comes down to a public health protection question.

"It is undisputed that secondhand smoke has significant health impacts," McCoy said. "The health risks for infants and children are particularly acute. Children's lungs are still in the process of developing, and they breathe a higher volume of air than you and I do because of their age."

Sen. Darin Peterson, R-Nephi, said the interior of a vehicle is a new realm of government regulation. In addition, the motivation seems to be correct a public ill, but there are so many other "construed circumstances" that could be addressed the same way.

"In my heart, this seems OK, but a car is private property, just like a house is, just like a piece of jewelry is, just like any other pieces of real or personal property," Peterson said. "My heartburn isn't the intent of the good. Justifying moving into the domain of private-property rights is an effort to do the right thing, but to legislate common sense has always been very hard for me."

Sen. Pat Jones, D-Salt Lake County, said smoke doesn't drift into thin air, even in much larger spaces than inside a car.

"The residue of smoke remains on the hair, the skin, clothing and is extremely harmful," Jones said.

Sen. Bill Hickman, R-St. George, said as important as protecting children's health is, he gets concerned whenever government starts legislating private activities.

"I can well envision next year or in the not too distant future looking at legislation to prevent smoking inside our private homes."

McCoy said he has been sensitive to the property rights rights issue. "As to the home versus the car debate, a car is the smallest confined space you can possibly smoke in."

Sen. Chris Buttars, R-West Jordan, said at the boys ranch he operated the intensifying of smoke in a vehicle is well understood by teens who use "hot boxing" to inhale marijuana. Even if only one or two smoke, with five or six in the vehicle, the smoke affects everyone.

"I've always been against this type of thing as far as government in peoples' lives," Buttars said about the bill. "But I've changed my mind when we're dealing with kids who have nowhere to get away from it."