In general, they have settled on a simple guideline: “run, hide, fight.”
The specific situation and location matters. “There is never going to be a universal rule for this,” said Bob Kolasky, an acting deputy undersecretary for the Department of Homeland Security who oversees active shooter training.
The department has published detailed advice, defining an “active shooter” as someone with a gun engaged in killing or trying to kill people in a confined and populated place.
The advice is based on actual cases. It can be chilling to consider, but the more prepared you are, the better your chances of survival.
“There is chaos,” Mr. Kolasky said. “The more you have got protocols in place, the more likely you are to minimize the damage.”
Look around you. Where are the exits?
When you hear gunfire, the first response should be to escape.
But would you know how to escape? Experts advise being familiar with quick routes out of your workplace. And whenever you are in a new location, take note of the exits. Use them if you are sure that your path will not take you in the gunman’s direction.
“If you can get away from that person, that is the best thing to do,” said Pete Blair, a criminal justice professor and the executive director of the Advanced Law Enforcement Rapid Response Training Center at Texas State University.
If on a higher floor, don’t use elevators; take the stairs. Windows are also an option. Students at Virginia Tech escaped the gunman in 2007 from a second-floor window.
If you believe you are in the gunman’s line of sight, run in a zigzag, or from cover to cover.
Do not pull a fire alarm. That creates confusion as to whether what is happening is a drill, as happened in the recent shooting in Parkland, Fla., where the gunman himself pulled the alarm, the authorities said.
An alarm could send people out of rooms and into large groups in hallways, where they would be targets, and draw emergency responders into danger as well.
Instead, yell “gun” or “gunman.”
Many workplaces and schools use drills to prepare workers and students for lockdowns and evacuations.
But if you are someplace like a theater, look for the exits yourself. Mr. Kolasky, who worked with the National Association of Theatre Owners after the Aurora theater shooting in 2012, said public service announcements in theaters often point them out. But they are only successful “to the degree that people pay attention,” he said.
Where do I hide?
If escape is not an option, you should hide, although Dr. Blair prefers to use the more active term “deny access” rather than what he calls “hide and hope.”
Dart into a room, closet, anywhere there is a door to lock, or at least to close and barricade. A room near an elevator is good because there is likely to be reinforced construction at the core of the building, noted Park Dietz, founder and president of Threat Assessment Group. Other office walls are often thin drywall.
You can also hide under your desk if there is no alternative. It’s not the best choice, but removing yourself from the line of sight and gunfire is better than nothing.
Playing dead is generally not a good idea, Dr. Blair said. Gunmen have been known to circle back and fire into wounded people or others on the ground, he said.
But in the 2012 Sandy Hook shooting, a teacher remained motionless after being shot in the leg and then escaped after the gunman had moved on. A student at Virginia Tech was shot while fleeing but kept going and survived.
“Keep operating if shot,” Dr. Blair said. “Try to get yourself out.”
What should I do after hiding?
Don’t stop to grab belongings, not even your cellphone. But if you do have one, once you are hidden, call 911, identify yourself and explain briefly what is happening and where. Then silence the phone or stop speaking but leave it on so the dispatcher can hear.
Turn off lights. Do not talk with others in the room if the gunman is nearby.
“Stay quiet as a mouse,” Dr. Dietz said.
Social media use might give away your location or help the attacker know where the police are, Dr. Blair warned.
Stay low in your hiding place, because a gunman is likely to open fire at torso or head-level, Dr. Dietz said.
If a barricade or lock is not available, Dr. Blair suggests not lying on the floor, because that would prevent you from the last resort: a surprise attack on the gunman if he bursts into the room.
The last resort: Fight.
Throw or use whatever you have at hand as a weapon against the gunman — scissors, bookends, chairs, a hammer, kettle bells, heavy doorstops. It’s not ideal, but it has helped, Dr. Dietz said.
If you are strong enough, wrestle or jump the gunman if he stops to reload, which could take just seconds.
That is how some stopped the gunman who shot former Representative Gabrielle Giffords and others at a supermarket near Tucson, Ariz., in 2011.
“There is no level of response that is going to be inappropriate,” Dr. Blair said. “I would encourage you to not go softly.”
All of the experts emphasized that confronting the attacker was a last resort.
“Most individuals are not trained to take down a shooter,” Mr. Kolasky said.
What if someone else is hurt or calls for help?
If you are safely hidden, think twice about opening the door again, even for colleagues or friends who are knocking or calling for help.
“Only open the door for someone else if you know the shooter is not in the area,” Dr. Dietz said.
If someone near you is bleeding and it would not jeopardize your safety, try to stop the flow, particularly if the wound is spurting arterial blood, which can lead to death within minutes. Use a tourniquet to slow bleeding if possible but be aware that untrained people can cause harm with one.
Apply pressure to stanch blood from less severe wounds, and elevate them. Run your hands down a person’s body to find injuries.
“Sometimes people get shot and don’t even realize it,” Dr. Blair said.
When help arrives, here is what to do.
When the police arrive, they might not be sure immediately who the suspect is. Put your hands up and spread your fingers to show you are not carrying anything that could be mistaken for a gun.
Do not hug the officers, ask them questions or request first aid.
Show them, do not tell them, that you are not part of the threat.
“It is not the time to communicate,” Mr. Kolasky said.