SAN FRANCISCO — At Yelp’s San Francisco headquarters, a keg refrigerator provides a never-ending supply of beer to employees, letting them drink as much as they like.

They just have to be comfortable with full disclosure: Workers badge in to an iPad application attached to the keg that records every ounce they drink.

“If you’re at the top of the leader board consistently, I don’t know if that’s a place that you’d want to be,” said Eric Singley, director of Yelp consumer and mobile products. “Luckily, that hasn’t really even been an issue.”

In a contemporary version of “Mad Men” and its bibulous ad executives, more dot-coms are embracing the idea of drinking at work. That means keeping bars stocked at all hours, installing kegerators and letting programmers tip back a few while they code. It also raises questions about the effect of alcohol on productivity and the safety of employees.

“Alcohol is sort of a slippery slope, because obviously you’d think it might impair their performance,” said Dalton Conley, social sciences dean and professor at New York University. “Many people can work after one beer, but I doubt many people can do serious knowledge work very productively after four or five.” While office parties and Friday-night beer busts are nothing new, the all-hours nature of startups means more employees blend their nightlife with work time. Drinking is an extension of that, said Joe Beninato, chief executive officer of Tello Inc., an app developer in Palo Alto, Calif.

“When you’re working at a startup, you’re working 24-7 and it takes over your life,” he said. “It’s not like it’s a wild fraternity party or something like that – we’re all adults.” When Tello’s iPhone app for rating customer service made it into Apple’s online store in February, the five-person company decided to celebrate. No matter that it was before noon.

“We got out the whiskey and everybody had a shot,” Beninato said.

Workers have a similar outlook at CrowdFlower, said Lukas Biewald, CEO of the San Francisco-based employment company.

“We do have a fridge full of beer, people do work late and drink out of it,” Biewald said. “When we first started, our office was like our home – we had leftovers in the fridge – and I think it’s an extension of that.”

It’s typical to see employees with a beer on a Friday afternoon, when the company lets workers demonstrate new projects, he said. CrowdFlower also occasionally gets kegs for gatherings it hosts for its community of developers and users.

Even so, the age-old problems of workplace drinking haven’t disappeared, said Robert Sutton, a professor at Stanford University. Some employees can’t drink in moderation or control themselves after imbibing, he said.

“I’ve been involved in workplaces that can be pretty dysfunctional, where people will start drinking a little too much at lunch,” Sutton said. “There’s like a bazillion studies that show when people drink, their performance is impaired, and there’s problems with absenteeism.”

Another danger: Women are at greater risk of sexual harassment at offices where heavy drinking is the norm, according to a Cornell University study.