# B Blast radius of mechanical explosion

#### MatNX

Summary
A container with pressurized air explodes in the air. What would the blast radius be? Wouldn´'t it just be the radius of the sphere calculated from the average air density and the mass of the air?
Imagine a container with compressed air ruptures. Inside is a metric ton of air, just very dense. If it explodes, ignoring fragments of the container and the ground, how would i calculate the blast radius? Do I need the Volume of the container or the density? I thought it might just be the radius of a sphere of air with the same mass but "regular" atmoshperic desity. But I don´t know, which is why I´m asking it here.

Related Classical Physics News on Phys.org

#### Nugatory

Mentor
You don’t start with the volume of air, you start with the energy released by the explosion. For back-of-the-envelope purposes this will be the same as the energy required to pump the air into the tank in the first place.

You’ll get an energy in joules, and google will quickly tell you that 4000 joules is about what you’d get from one gram of TNT, so you can convert your tank explosion into an equivalent TNT explosion. There’s plenty of online data about blast radii in those terms.

If you do the calculations right, you will conclude that highly compressed air is more dangerous than you might think. A typical military hand grenade is lethal out to about five meters and dangerous at ten times that distance... and a full scuba tank makes for quite a bit bigger of an explosion.

[Edit: and I should add that a metric ton of air is much much more than what goes into a scuba tank.]

Last edited:

#### MatNX

Ok, thanks! That was really helpful!

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving