Brmbag is a project to slow down/stop bullets and shrapnel using ultra-tear resistant air bags. These can be either ceiling mounted bags or personal air bags.

There are basically two factors that determine whether the brmbag would work at all.

1. Can the bag detect a blast and deploy fast enough to get in the way?
2. Can a bag filled with air stop a fast flying object?

To answer the first question, I'll start by saying that shrapnel is propelled by an explosion, and so are airbags. While airbags do suffer from much higher air resistance, there is no physical reason why an airbag cannot deploy as quickly as the shrapnel from a bomb blast. The limiting factor in an airbag's speed is that it has to deploy slowly enough not to injure or kill the people that it is supposed to protect.

Airbags in cars typically deploy at a speed of 200Mph or 90m/s. Normal bullets fly at between 120 m/s and 1,200 m/s. The rate at which the airbag must deploy is dependent on the distance from which the bullet is shot. If we are trying to prevent the president from being assasinated by a sniper who is 200 meters away, an airbag traveling at 90m/s can inflate to 15 meters in diameter before the bullet reaches the president! However, an airbag will probably never stop a bullet from a handgun shot at point blank range.

As for whether the airbag can actually stop a bullet, I don't know that yet, but physics guarantees that it can, at least, slow it down.

Personal airbags to protect “VIP”s are almost certainly possible. They don't have to deploy to a very large size in order to cover the head and face, and the body is already covered with a bullet proof vest. However, while such air bags might make commercial sense, they are of little interest to brmlab, our president is a ninja from the matrix and can easily dodge such assasination attempts.

It also seems likely that airbags attached to the ceiling, or mounted on posts would be able to limit the blast radius of shrapnel from a bomb blast. While it seems impossible that they would protect people directly adjacent from the bomb, they should be able to prevent the kind of disaster scenarios where a suicide bomber kills dozens or hundreds of people.

More difficult would be to stop bullets with ceiling mounted bags.

Perhaps the most critical factor in such a system is having a fast detector which does not cause a lot of false alarms. While it may seem that effectiveness of the airbag system is critical, it really is not. Even if it only works in a small percentage of cases, if it saves lives, the technology may still be worth it. However, if the bags are constantly inflating, or if some kid with a cap gun can set them off just for laughs, we may have a problem.

That said, if a kid walks into a shopping mall and starts firing a cap gun, it already causes the entire city to shut down. One time, the metro station near where I live was shut down for a whole day, simply due to a single anonymous SMS. And when you go on TOR, you will find multiple CaaS (Chaos as a Service) providers which charge by the hour for lockdowns and SWAT team visits.

If such air-bags demonstrate themselves to be capable of truly improving safety, this can only lead to a less jumpy security system and may lead to fewer, rather than more, prank events.

I think that the most compeling reason to be interested in a project like this is political. Efforts to prevent terrorist attacks seem to always take away the freedoms and privacy of everyone. I feel like we are always looking up to the government to protect us from terrorists and this constantly expands government powers in a way I don't like at all. If we are able to take responsibility for our own security in an effective way, we may be able to both increase our freedom and our safety at the same time.

Also, if these things turn out to work, and get installed in every public space in the world, that's like a gazillion dollar market opportunity.

In order to detect a blast, one cannot rely upon sound. Bullets travel near or above the speed of sound. An optical solution is a must. I also think that looking for muzel blasts is a no-go, as these can be muffled quite effectively. Rather, I would trigger the airbag any time we detected an object moving at or above say 75m/s.

Perhaps this could be done by having an LED blinking at a high rate of speed and measuring reflected light levels, if the light levels change to quickly, than we have detected a fast moving object. Another option would be to do something similar but with a rotating flat beam of light.