Washington - Federal workers likely felt the chill on Monday after President Trump issued a hiring freeze that would be "applied across the board in the executive branch," an order that reinforced candidate Trump's frequent promises to "drain the swamp" and reduce the federal workforce.

Yet the freeze left open plenty of exceptions. Jobs that agency heads say have national security or public safety responsibilities are exempt. So are military jobs, though The Post's Lisa Rein reports that it's unclear whether that applies to civilian defense roles or just uniformed personnel. The memo also says the Office of Personnel Management may grant exemptions when they are "otherwise necessary."

Such exemptions, however, are just one reason human resources experts warn that hiring freezes can be damaging to the morale of the people left to pick up the slack. If hiring freezes lead to frustration and burnout, it's usually the top performers who leave first. And limiting the number of people who are hired, they say, can result in more risk aversion -- and therefore, less innovation -- while driving stressed and overwhelmed workers to take shortcuts.

"If you've got this problem of people being overworked, and they end up finding workarounds, it can cost money in the long run," says Peter Cappelli, a professor at the University of Pennsylvania's Wharton School.

Trump, of course, is the corporate president, a real estate magnate who touts his business know-how and dealmaking chops. Yet few businesses use across-the-board hiring freezes anymore, says Brian Kropp, who leads the human resources practice at the consultancy CEB. "Most companies don't do it," he says. "The world changes so quickly that you need people with particular skill sets."

Read also: How to decide which career to choose

Of course, most businesses are looking to grow, and as a result, eventually expand headcount after they get out of the rough spot that led them to suspend hiring. Trump, meanwhile, has said he wants to reduce the size of the federal government through attrition. If lower morale leads to even more departures, it could serve his aims.

Yet until that happens, managing the expectations and motivations of the people who remain will be critical. Making a freeze across-the-board, but allowing for exceptions, can be a recipe for bickering and infighting.

"If you start making exceptions, it can create this huge sense of inequality -- why did they get it through and mine didn't?" Kropp says. Former personnel chiefs told The Post's Rein they would expect agency chiefs to interpret the exemptions broadly.

Best jump first

Meanwhile, when companies put in hiring freezes that overload workers, it's typically the best people who jump first.

"The people who are most marketable are the first ones to go out the door," says Wayne Cascio, a professor at the University of Colorado Denver's business school who has studied downsizings and restructuring.

For Trump, of course, "the best people," as he likes to say, probably aren't the ones he wants to lose. And among the people who remain, there could be burnout or frustration. Kropp says CEB's research shows that hiring freezes can cause a productivity drag of 5 to 15 percent. And the effect could particularly hit federal workers: While many see their jobs as having a sense of purpose through public service, surveys show that government employees, on the whole, lag well behind their private sector counterparts when it comes to employee engagement.

Still, others say that if the hiring freeze is relatively short-lived, its effects may be limited. Trump's order says the hiring stop is scheduled to last 90 days, beyond which the Office of Management and Budget "shall recommend a long-term plan to reduce the size of the Federal Government's workforce through attrition." If individual workers don't feel it personally affect them or their responsibilities, Cascio says, "in the short term there's probably not going to be much of an impact" on morale.

Read also: Striking a balance between life and career

The effects could be felt in other ways. When there's a hiring freeze on, people tend to grow more wary of taking chances and work less creatively, Kropp says. "One of the things we've seen occur a lot," he says, is when organizations "start cutting budgets, the levels of innovation fell pretty dramatically. Employees we surveyed said they weren't going to try something new because they thought they were going to get punished."

And if workers feel under stress and overwhelmed, they may provide slower service or find workarounds to help them get things done. Indeed, an often cited 1982 Government Accountability Office study found that past hiring freezes actually ended up costing more.

"It's not just the hours of the work," Cappelli says. "It's the stress of doing your own job and someone else's job you don't really want to do."