Chances are likely that where you live there is some kind of natural disaster known to man that might happen there. Drought, flooding, fire, earthquake, tsunami, volcano, ice storm, snow storm, hurricane, tornado...the one common thing about living on the planet Earth is that there are lots of potential disasters--natural and otherwise.
As a manager, people see you as an authority figure. Stop laughing. I'm serious. When a disaster happens, you are more than likely still going to be in charge.
Does this mean you need to be a Firefighter, Tornado Chaser, or Ghost Hunter? No. But because these things could happen, you need to be familiar with the work place policy on the most common types of disasters. Further, if the company doesn't have company-wide drills, you need to work with HR to come up with appropriate drills so your team knows what to do in the event of a fire, earthquake, etc. You may also need to designate yourself some help in those situations, such as safety managers or floor fire marshals, or whatever your team calls them--people that help you make sure everyone gets out and gets out safely and knows, at least a little, of what to do in an emergency.
As a manager, unless the job specifically requires it, you typically don't have to know CPR. As a person, and especially as a person that other people will look to in an emergency, it might behoove you to get some certified training so you are better prepared in the event of an emergency, whether its at work where you're the boss or on the road as you are driving by. A little information can make it a lot easier to sleep at night, and could be a life or death difference for the people you meet.
Once you know what to do in the common workplace emergencies, make sure to set up drills, etc. quarterly to keep your folks aware of the issues. If this means swapping out the water in the earthquake kit (that stuff isn't potable forever) or doing your own emergency fire drill, or whatever, be sure to bring up safety at least once each quarter.
And now, what about the non-standard workplace emergencies? For example, if you live in a place where it doesn't snow a lot, and suddenly it starts snowing, what's your policy on people leaving early or working from home? Does the heat stay on at night in case people get trapped? If not, is it easy to change that? These questions also apply to flooding or major, major traffic issues. It's good to know what food, blanket, and shelter options are available in your building. Human Resources and Facilities can be your guides in this area.
Generally, because I live in the Pacific Northwest, if it starts to snow, I send people home. If they can work from there, fine; if they cannot, they can make the time up (or not be paid for it) as they choose. People in Seattle readily abandon their cars on perfectly good freeways and streets with as little as two inches of snow, which means your people need all the help they can get to get home safely. Obviously, use your own judgment, but think about these things before they happen, so your judgment is made in the unpressured light of day, and not, say, in a temporary black out while folks are looking for flashlights.
Finally, there are the non-standard severe emergencies. Massive power outtages; tornadoes, tsunamis of hurricanes where those things don't normally occur; or even, sadly, human-made emergencies, where a hostile person breaks into the office and does violence. Most workplaces have a policy on what to do if a hostile person is on the premises; most people don't care to review the policy, because most people cannot imagine that someone that they know could get violent.
I urge you, as someone who came close to having a hostile in her work environment, read those policies. Think about what you'd do, to protect yourself and to protect others. No matter how remote the chance, it's severe enough that if it ever happened, information that you have could be the difference, literally, between life and death. I can't offer advice here--I know what I'd do. But you need to select what works for you and yours.
In terms of the other unimaginable things, well, they are unimaginable. Here, however, are a few tips that might help, based on the unimaginable happening when I was running the technical support department of a game company in Mountain View, CA.
See, the sky got very gray. Lots of electricity in the air. News reported tornadoes touching down around the area--specifically, one was headed for Moffet Field, across the freeway from my building. That's very close in tornado terms.
I had a youth spent in Tennessee where as kids we drilled on what to do if a Tornado came through. My co-worker, in charge of the accounts team, did not have that training. The "pit" where customer support spent is hours, was a glass room with dark paper over most of the windows that did not open.
Step 1: Get Information
Had I not already known what to do, I had a room full of computers, so the first step when something unimaginable happens is: get information. Both about the phenomena in general and what's happening to you in particular. In our case, we had one guy with the door open staring at the freeway and the skies, and another two folks checking local weather. If I hadn't known what to do, I would also have had one of them looking that up. Sometimes you have time, sometimes you don't, but if you do, get as much information as you can.
Step 2: Find an Authority and get Their Input
I don't mean an authority in the management chain, but an authority in the type of event, if possible. In our event, I was that authority. The accounts manager was having everyone get under their desks and cover their heads with their hands. Prudent if this was an earthquake, but likely to kill people since all their desks were in front of windows and this was a tornado (which are known for altering the air pressure and shattering windows into large pieces of death glass). Fortunately for us, our boss had been complaining for the last month about being the only office with no window in the building. This made her office, and the hallway immediately outside it, the safest parts of the building.
Step 3: Explain the Plan and then Execute It, ASAP.
To do what little I could for pressurization issues, we propped the doors to which we had access (outside and inside) open to make it easier for the air pressure to equalize. I explained what we were doing as we did this, and where we were going and repeated, throughout, that we would be okay. Not, necessarily, because I knew it to be true, but because of all the lies you go to hell for, this is not one of them, in my opinion. If we were, and I was right, woohoo! If we weren't, and I was wrong, people would have worse things to dwell on than my lie.
Then I marched my team and the accounts team to my boss's office. I made a point of marching them past the other groups in the office.
Step 4: Try to Help Others if You Can (but keep in mind that they might not know what you know)
Customer support is very low on the totem pole, so I couldn't exactly tell everyone to stop working and follow me (they would not have) in the rest of the company. But, watching us, silent as ghosts, march away from our stations and the long way to my bosses's office caused enough people to come up and ask what we were doing that by the time we got to our destination, we had the majority of the building's occupants with us, and people higher in the org scouring for the remaining few.
Then it was a matter of kneeling on the floor with center of gravity far down, head lightly against the interior walls, and hands and arms protecting as the storm raged.
Step 5: Ride it Out
It was tense and quiet and dark and warm and scary. And then it was over. The tornado missed our building. The power was out. There were no emergency generators. But we were able to visibly see the funnel cloud in the distance moving away. Now, they can turn around and come back, but it was breaking up, so I wasn't concerned. If you have a subject matter expert on hand during your own emergency, check with them. Not everyone knew that those funnel clouds can turn right around and come back.
Step 6: The Aftermath is Not Going to Be Anymore Fun than the Actual Emergency (and probably less)
You survived. Yay! You need to wait for help or go get help. You need to work with the other leaders in your group to take care of the people who may have gotten hurt. You need to arrange for people to go home and/or call their families. You need to do this while everyone is pestering you about what to do next because you seemed to know what to do before which means you probably know what to do now...
In our case, the power was out, so all the phones were out except for a few cell phones (this was the 90's when they weren't as ubiquitous as today). Marketing had the cell phones, but would not let us use them--they were calling their families and their customers.
I marched the customer service group back to our area. We had a fax machine; that meant we had one analog line (no additional electricity required). We also had an old analog phone in a cupboard somewhere. It was dutifully dug out, and then my team was allowed to make a two minute phone call, each, before we notified the rest of the building a regular phone was available. I could do that because there was no one hurt; if there had been, even though folks had cell phones, I would have turned over the analog phone immediately, as it was more likely to get through and be reliable than the cell phones. Note, in an emergency today (and not the 90's like mine), cell towers will get quickly overloaded, so try not to use the phone if you can avoid it, and if you must, use a land line and try to call a land line.
After you've had contact with officials--police, CDC, medical personnel, whomever--and its safe to release folks, let them go home. Even if you have to have a skeleton crew, let them go and come back (if that is possible). Emergencies are SCARY. People aren't useful to you when they're worried about their loved ones, and they don't stop worrying about their loved ones just because they heard a voice on the phone. Looting is also a common issue for many natural disasters, and people want to be with their people to protect them and to feel safe, and not necessarily with the folks that they work with every day.
In our case, I waited until the power was on with a friend having sent everyone home, then set up the call lines to let people calling know that there had been an emergency and we'd be back tomorrow. I set up the same message for the email auto responder. Then I went home, too.
In summary, being the boss at the office also means that people have potentially unrealistic expectations of you when a disaster hits. When people get scared, their brains stop working, and so you need to put them and yourself through exercises so that they have a chance to get those brains working again, and so that you reduce the chances of anyone, especially you, getting hurt in a disaster. Of course, after you've all survived, things get a little worse before they get better, but they will get better...an you'll still be the boss.