Attorney Miller says he recommends his contractor clients explore a "hybrid policy" that offers more flexibility in testing than zero tolerance. Such policies maintain strict new-hire procedures and more testing for newer employees but offer longer-term workers a second chance.

"They ought to know better, but you may not want to lose a 10-year employee based on one mistake," he adds.

Kurt Klanderud, president of GH Phipps, says, "We will, of course, apply our procedures, but we are aware of the need for some flexibility as situations come up."

Many firms will not discuss their drug-testing protocols, and some won't comment on legalization at all. "We're going forward like it hasn't happened," says a human-resource director for one Colorado firm.

However, most experts caution against denial.

"Legalization doesn't change employers' rights, and it shouldn't change employee practices, at least not in Washington," says Scott Gingras, an attorney with Winston & Cashatt, Spokane, Wash. But he encourages firms to remind employees more often about company drug policy, federal law and the dangers of impairment.

"There is honest confusion with some employees who ask, if it's legal, how could it be in violation of company policy?" Miller says.

Many also are asking what constitutes "impairment." Under Colorado and Washington driving laws, impairment means having five or more nanograms of THC (delta 9-tetrahydrocannabinol) in the bloodstream.

The testing limits for many construction firms are based on that amount, although some, such as Haselden, set the limit at four nanograms. "Science has not caught up with this issue," Miller says. That's because marijuana can stay in the body for four or six weeks, even if an employee hasn't toked in that time.

Firms such as PCL say they may increase random testing.

"Not many people out there care whether someone lights up on their own time as long as they're not impaired on the job, but we have to," says Rich Baldwin, PCL director of health, safety and environment.

"We are aware that the workers who wanted it before [legalization] were getting it anyway."