The kinetic energy of the explosion is converted to heat, light, blast (pressure), EMP and initial radiation. The height at which a bomb is exploded hugely determines the amount of each of these effects as also the fallout effect (which is responsible for many times more casualties than the direct blast and heat effects). All weapons are calculated to be exploded at the optimum height to maximise the blast / heat effects as well as for maximum fallout effects.

BLAST (PRESSURE): Within seconds after the explosion, the expansion of intensely hot gases, at extremely high pressures, causes a shock wave to move outward at extremely high velocity. Pressure rises very sharply at the moving front and falls towards the interior. This OVERPRESSURE decays with distance and depends on the bomb yield. After a certain distance, the overpressure becomes negative, sucking air and lot of material towards the explosion instead of pushing it away. Most of the material damage is done by this blast wave. The overpressure can be thousands of Kpa, whereas only 3.5 Kpa is sufficient to break glass.

Weapon Yield (MT – megaton)	500 m		1 Km		200 Kpa Red Zone starts (100% shelter safety)		5 Km		10 Km		3.5 Kpa Yellow Zone starts (Safety from blast effects)
1 MT	2900 Kpa		500 Kpa		1.65 km		22 Kpa		7.2 Kpa		19 km
2 MT	5800 Kpa		825 Kpa		2.05 km		32 Kpa		10 Kpa		23 km
5 MT	16300 Kpa		1900 Kpa		2.8 km		54 Kpa		17 Kpa		32 km
10 MT	16500 Kpa		3700 Kpa		3.5 km		85 Kpa		25 Kpa		40 km

It is to be noted that only military or very costly civilian shelters can survive in the black zone. From 200 Kpa to 3.5 Kpa, (i.e. in the red and orange zones) everybody must be in a blast protection shelter. Beyond this (in the yellow zone), everybody must be in a fallout protection shelter.

The blast is actually in two parts – the air blast and the ground blast. The air blast decays with distance faster than the ground blast, which may continue for longer distances. The air blast can measurably and significantly compact the ground or surface (air slap). The ground blast is like an earthquake and causes huge lateral damage. Due to very high wind speeds, a dynamic pressure is created which is much higher than the overpressure.


Comparison between sample overpressures, dynamic pressures and wind velocities (at sea level):

Peak overpressure (Kpa)	Peak dynamic pressure (Kpa)	Maximum wind velocity (Km/hr)
1380	2275	3340
1035	1530	2860
690	850	2270
495	510	1880
345	280	1500
205	115	1080
135	56	808
69	15	470
35	4	260

Note the extremely high wind velocities. These winds will clear most of the above ground structures in entirety and are one of the major reasons for citing shelters underground.

The immediate area of the blast will have a crater, a fracture and a plastic zone for up to about 1.5 km radius, depending upon the weapon yield.

THERMAL (HEAT) WAVE: Fusion reactions require millions of degrees of temperature to start. In turn they themselves generate extremely high temperatures. Approximately 35% of the bomb’s energy is converted to heat energy. For a 10 MT (megaton) bomb, plywood with an ignition point of 67 J/cm2 will ignite at 20 km. For the same bomb skin burns will be 3rd degree at 20km, 2nd degree at 25km and 1st degree up to about 30km. Apart from these direct effects, the initial temperatures can cause massive amounts of secondary fires. Assisted with wind and ideal conditions, these fires can travel very fast and cause immense amount of material damage and human casualties, including from release of poisonous gases.

INITIAL RADIATION: All radiation emitted in the first 60 seconds is called the initial radiation. It is the highly injurious nature of these radiations and their long range that make them so significant. They cause a considerable proportion of casualties. However, their range of destruction is nothing compared to Fallout radiation. For a 10 MT bomb, radiation due to gamma rays becomes negligible at 6 km, and due to neutrons becomes negligible at 4 km. Due to inelastic and elastic scattering (such as sky shine), radiation comes not only from the direction of the explosion but from all directions.

Radiation is of the following types:

Alpha: positively charged nuclei of helium atoms; relatively heavy and easily stopped.

Beta: negatively charged electrons; more penetrative than alpha.

Gamma: genuine electro magnetic radiation with highly variable wavelengths and high energy which depends on the source. Great penetrative power. Very harmful.

Neutrons: neutrally charged and heavy particles. Free neutrons released have high mass and great energy and are very harmful to life as they destroy human cells on collision. With every collision of a neutron with other atoms in the atmosphere, more gamma radiation is emitted. Gamma rays emitted from collision of neutrons with nitrogen atoms in the atmosphere are most harmful due to extraordinarily high energy.

FALLOUT RADIATION (The biggest killer):

In any fission related bomb, a considerable amount of the original fuel is unconsumed. This is the main cause of the deadly nuclear fallout. In a near ground explosion, the fireball will pick up considerable amount of material from the surface, part of which will vaporise. However most of it will melt, producing an enormous quantity of molten particles on which the radioactive products from the explosion will later condense during cooling. This fireball continues to rise, maybe till 20 km height but as the ascent slows down, an ever increasing number of radioactive particles fall to the surface. The size of these particles ranges from very fine dust to several hundred microns. This is the Fallout. The largest particles fall closer to the explosion area but the smaller particles can travel with the winds to hundreds of kilometres before falling, while still being highly radioactive.

The fallout reaching the surface in the first 24 km is called early fallout. The rest is called delayed fallout. The early fallout consists of more than 300 isotopes of 36 elements. As more fallout arrives on the surface of the earth, the dose rate of radiation increases. The direction, distance and strength of fallout is unpredictable and dependant on many conditions. Generally it has to be measured to be ascertained. THE ONLY CERTAINTY IS THAT IT WILL SPREAD OVER THOUSANDS OF SQUARE KILOMETRES. AS AN EXAMPLE WITH OUR 10 MT BOMB, AFTER JUST ONE HOUR FROM EXPLOSION, IN IDEAL WIND CONDITIONS, A DOWNWIND AREA OF 57,000 SQ.KM CAN HAVE RADIATION MORE THAN THE SAFE LIMIT OF 0.3 GY/HR.

Until it is safe to come out, persons must take shelter in Fallout shelters. This is generally true for about 21 days. Most fallout is invisible to the eye and cannot be detected without appropriate detectors. Fallout on clothing or other articles can also contaminate other objects which come in contact or vicinity. This decontamination of fallout is an essential procedure during the sheltering period and forms part of our survival training package.

The delayed fallout consists of very fine particles and travels to very long distances. It does not have any immediate effects but is responsible for many long term illnesses and cancers.

EMP: Strong electric fields are produced momentarily, which have a very broad spectrum of frequencies. This pulse carries a considerable amount of energy. Once in contact with cables or other conductors, it sets up very high voltages and strong electric currents. For a 10 MT bomb, it can destroy circuits and have effects till about 15km. It can disrupt communications upto about 90km. Some types of nuclear bombs are exploded very high up in the air to maximise the EMP effects over longer distances without the blast effects.

Four main types of nuclear bombs

Fission Bomb: Energy released from splitting of nuclei. Usual fissile material is Uranium or Plutonium. These have a limitation on size due to issues related to critical masses of these elements. Very few modern weapons are of fission only type. They produce a lot of initial radiation and a lot of fallout radiation due to the fission material being radioactive.

Fission-Fusion Bomb: A small amount of fission is used to raise the temp to millions of degrees for fusion to take place. However, fusion takes place between Hydrogen, Deuterium and Tritium neither of which are radioactive. Energy released is many times more than a fission reaction and these bombs have much more severe blast and heat effects. No size limitation. Due to only small radioactive fission material, and a large amount of non-radioactive helium, these weapons produce a lot of initial radiation but not much fallout radiation, which is the real killer. That’s the reason they are called ‘clean’ bombs.

Neutron Bomb: A variant of a Fission-Fusion bomb. These have been tuned such that there is lot of Fallout radiation but lesser blast and heat effects.

Fission-Fusion-Fission Bomb: These are designed for maximum blast and heat effects and also for maximum Initial and Fallout radiation effects. A small fission reaction triggers the fusion reaction, which in turn triggers another larger fission reaction, thus ensuring maximum blast (from fusion) and maximum fallout (from the second fission). Thus they are called ‘dirty bombs’. Most bombs are of this type.

Note: As testing of nuclear weapons was banned in 1962, most of the data available for effects of nuclear explosions are based on older bomb designs. Where available, newer data has been incorporated. However, modern bombs are much more powerful and the effects and distances described above can be taken as a minimum. Also, for reasons of confidentiality and plagiarism, a lot of data and calculations have not been shared here, but may be selectively shared during signing the contract and site surveys.