A ground blast produces less radiation than an air blast. If the target is a city with a big population, air blasts are used so that radiation comes down in the artmosphere over a wide area, killing a larger number of people over time.
Back when I read James Herbert's 'Domain' (his third 'Rats' novel) I did a lot off reading up about radiation and the effect of a nuclear explosion. Can't find those notes now, so this comes from a webpage quoting from the 'World Book of Encyclopedia',
http://library.thinkquest.org/26742/nuclear.html
1) When an atom bomb explodes a blast wave is created from a cloud of high temperature gas and dust under extremely high pressure. This cloud is formed only a split second after the bomb explodes. From ground zero the blast wave causes the most destruction of any of the effects of the bomb.
As the blast wave moves forward it creates overpressure, the atmospheric pressure above the normal pressure level. The overpressure is what destroys most buildings in an explosion. The blast wave is also accompanied by high winds, which can reach up to 400 miles an hour as far as two miles from ground zero.
(I think this refers to air blasts. Ground blasts, as in KOTCS, cause sideways pressure, blowing buildings sideways rather than downwards - hence the fridge flying out!)
2) Thermal Radiation, consisting of ultraviolet, visible, and infared readiation, is what causes severe skin burns called "flash burns." The ultraviolet radiation is quickly absorbed by particles in the air, and therefore, is contained before it does any real harm. The visible and infared radiation can cause eye injuries and severe "flash burns." Thermal radiation is also responsible for starting fires. Thermal radiation is hot enough that it can ignite old newspapers and dry leaves. Protection from thermal radiation can be obtained from walls, buildings, trees, light colored clothing, and other landscaping features.
Thermal radiation only lasts about ten seconds, but can cause second degree burns and blistering as far away as eleven miles from ground zero. Being that it only lasts about ten seconds, the thermal radiation would only char objects like thick pieces of wood, plastic, and heavy fabrics- it would not burn them up completely.
3) The initial radiation, which is emitted within a minute after the intitial explosion, dosen't extend very far away from ground zero, and diminishes rapidly in strength the farther away from ground zero you are. Initial nuclear radiation is composed of neutrons and gamma rays. The neutrons and some gamma rays are emitted from the bomb almost simultaneously. The rest of the gamma rays are given off from the mushroom cloud created by the explosion.
It's implausible, but so are many of Indy's escapes. He has always relied on the Jone luck for eery cliffhanger. This time he might have used up a bit more of his 'luck reserve'. Some freakish things can happen. The blast wave blows the fridge clear before the thermal radiation or intial radiation can take effect. Then the only thing Indy has to worry about is landing without pulping himself, and since this
is pulp, he gets away with that, too. The fridge must absorb all the impacts, and Indy is packed so tightly inside that his body is protected.