A nuclear weapon can produce a burst in three completely different ways. The different types of bursts are subsurface, surface, and air. The type of burst directly affects your ability to survive.
A subsurface burst occurs completely underground or under water. Of the three, this is the best case scenario as its effects remain beneath the surface or in the immediate area of the blast. Typically the surface will collapse into a crater immediately above the location of the burst. There is little to no chance of being exposed to radiation unless you enter the area of the crater.
An airburst occurs in the air above its intended target. The atomic bombings of Hiroshima and Nagasaki were examples of this type of attack. This type of burst provides the maximum radiation effect on the target, and is, therefore, the most dangerous to you , in regards to your immediate personal survival. With an airburst you should expect to see enormous shock waves, searing heat, a blinding light, fires, and extensive damage.
A surface burst occurs on the ground or water surface. This type of blast produces the most fallout and poses the most long term health effects. This type of blast is the worst of the three due to the large amount of radioactive fallout it produces. A survivor of this type of event would be forced to seek shelter for a long period of time and would experience a greater risk of exposure to radiation. While the airburst is the most dangerous a surface burst poses the greatest overall nuclear hazard due to the amount of fallout produced.
The Initial Effects of Nuclear Weapons
You Can Survive a Nuclear Blast
Is the Threat of Suitcase Nukes Real?
A Nuclear Bomb Just Detonated...Now What
Protect Yourself From a Nuclear Blast
Can One Nuclear Weapon Cripple America?