First off, let us just say that hopefully none of you ever find yourselves in a situation wherein you have to defend yourself from being shot on the job. Having said that, you probably have at least of few colleagues who can't be completely ruled out on going postal one afternoon, co-workers who have a knack for pissing people off and/or a boss whose net-worth makes him and his staff good hostage candidates. Preventative measures (a receptionist who keeps an AK-47 in her bra) can only go so far and if the shooter is already in the building, perhaps at his desk on the trading floor, you've got a situation probably few know how to deal with. Luckily, the NYPD has put together a handy list of tips should the guy or gal who sits 10 feet from you be easily set off.
Tip #1 "Avoid the shooter and evacuate immediately."
Tip #2 In the event fleeing the scene is not possible, your best "Plan B" is to "hide behind a filing cabinet." According to a study, "cubicle partitions provided no protection from bullets or shotgun pellets, and desks were little better. But file cabinets stopped bullets from a .38-caliber Smith & Wesson, a 9mm Glock and a shotgun. Only bullets from an AK-47 passed through."
Tip #3 Consider "barricading and hiding in a predetermined safe room," where you should "silence your cell phone" and remain quiet.
Tip #4 As a last resort "try to take the gunman down." The NYPD recommends confronting him "with physical force as quickly and as aggressively as possible," using "pens, staples, chair legs, anything you can get your hands on, as an improvised weapon."