When is it OK to catch some shut-eye on the job?

Workplace snoozing has been the topic of an awful lot of water-cooler jesting lately — at least among those awake enough to remember their conversations.

First, there were a rash of reported incidents of air-traffic controllers nodding off during late-night shifts, though no serious accidents occurred. Then, Vice President Joe Biden became a target of nationwide fun after he nodded off during his boss' noontime budget speech.

The notion of napping on your employer's dime seems to violate every aspect of the work ethic instilled in Americans from the nation's earliest days. But sleep experts say there are a few circumstances in which catching a few Zs in the old sweatshop is not merely acceptable, but desirable.

Dr. Susheel Patil, a deputy director of the Johns Hopkins Sleep Disorder Center, thinks naps should be scheduled for people who work the graveyard shift, particularly when — like air traffic controllers — they have jobs requiring maximum mental alertness.

And Jeanne Geiger-Brown, a director of the Work and Health Research Center at the University of Maryland's School of Nursing, says people slated for extremely long shifts should also get a regular chance to catnap. Medical residents, for instance, currently are on call for up to 30 hours at a stretch, and may or may not sleep for a portion of that time.

"Industries are now beginning to look at fatigue as part of their risk-management plan," she says. "Some people think it's silly to allow workers to sleep on the job. But it's even sillier to have employees so impaired they can't function."

History and popular culture are rife with notorious nappers:

Cartoon character Dagwood Bumstead has been dozing at his desk at the J.C. Dithers Co. for the past 78 years.

Winston Churchill, the legendary British stateman who shepherded his island nation through World War II, once said: "When the war started, I had to sleep during the day because it was the only way I could cope with my responsibilities."

And former President Bill Clinton was captured on YouTube after he famously drifted off in January 2008, during a Martin Luther King Day celebration in a Harlem church.

Geiger-Brown suspects that drowsy politicians fall into the category of people who slumber involuntarily in the middle of the day because they've been working into the wee hours.

"Sleep is a biologically active process," she says. "Your body has to have it. If you don't give your body sleep, it's going to find a way to take it."

Extreme sleep deprivation, she says, results in a phenomenon known as "micro-sleeps" in which the person nods off for periods ranging from 500 microseconds to a few seconds.

During these micro-sleeps, people appear to be awake. But their brains have stopped processing information — occasionally with disastrous results.

"In the old days, if a worker fell asleep on the highway on his way home and killed another motorist, he was the only person liable," Geiger-Brown says. "But there have been a few recent examples of people have won judgments against employers who should have known their workers were too tired to drive. And some of those judgments have been for more than a million dollars."

So when Dagwood grabs 40 winks, he might actually be doing the J.C. Dithers Co. a favor. Nor is he the only employee ever to nap while his supervisor's back is turned.

According to a 2008 study by the Virginia-based National Sleep Foundation called "Sleep Performance in the Workplace," 29 percent of workers acknowledged either becoming very tired or falling asleep while on the clock.

Though just one in 10 succumbs to the temptation to take a nap, 24 percent of employees said they would put their heads down if their bosses allowed it.