BLAST

by far the most important effects from an airburst atomic bomb is that of blast it causes widespread damage from total devastation in the neighborhood of ground zero to light structural damage up to a distance of two miles let us now examine this shock wave of blast more closely and see how and in what form it achieves this effect the atomic bomb is likely to be detonated above the ground in order that its maximum effect can be achieved over the widest possible area if the bomb were to be detonated too near the ground the target area close to Ground Zero would be pointlessly over devastated and the tremendous blast effect thereby wasted when it could have been used for creating much more widespread damage it is for this reason that the height of detonation is determined in relation to the power of the bomb the nature of the target must of course also be taken into consideration the more solid construction of modern cities would call for a lower height of detonation or a more powerful bomb than that chosen for buildings of later construction such as bears in Japan an important factor which will influence the chosen height of detonation will be the effect obtained by what is called the reflected shock wave when an explosion takes place above a reasonably level surface the shock waves are reflected back from that surface as if it were a Miller the combined waves original and reflected joined together to form what is called the Mach wave it is because the reflected wave reinforces the original wave that enhanced blast effects are achieved by an airburst atomic bomb but with atomic blast the pressure in an outwards Direction lasts for a comparatively long time so that any structures or parts of structures that are going to fall will do so before the suction effect of the blast wave reaches them thus the effect is like a very heavy push that will distort steel or reinforced concrete frameworks with radius of half a mile from Ground Zero it should be understood that with atomic blast the scale of effect is so great that there is much less shielding from blast than is commonly supposed assuming that the bomb used is of nominal size and that it is detonated at a height of one thousand feet we will now apply these known effects of blast to several types of buildings at varying distances from Ground Zero we'll take an average two-story domestic house of brick a multi-story brick building a multi-story steel framed building and a single storey light steel framed Factory with corrugated iron or asbestos sheeting within the course of a mile of Ground Zero these buildings will all be demolished the two-story house will be pushed over and flattened so that the debris lies evenly spread some three feet deep the multi-story brick building is the same except that the depth of rubble will be proportionately greater the multi-story steel frame building will be pushed over away from Ground Zero and the brick wall panels will be blown out the concrete floors will be broken and the overall depth of the debris will be in the order of 3 feet per storey height the single-story steel frame factory will suffer much the same but the depth of debris will de less now take those same buildings as if they were situated 3/4 of a mile away from Ground Zero the two-story house suffers heavy damage and will be classified as damaged beyond repair although some of the walls and floors might still distending the multi-story and more solidly constructed building would also have severe damage probably beyond repair the nature of the damage and the amount of debris therefrom would vary considerably with the direction of the blast in relation to the characteristics of the building the multi-story steel-framed building at this range suffers much less damage the steel frames are unlikely to be even distorted but some of the brick panels facing the explosion would probably collapse the concrete floors would be undamaged and the debris would not be severe the steel frame factory being of much weaker construction were almost certainly be distorted and the sheathing from the walls and roof will be blown off but sheeting does not produce a serious debris problem lastly we will take the same buildings as if they were located at a mile and a half from Ground Zero the dwelling-house windows broken tiles off the roof and maybe a chimney part missing there will be considerable damage to internal fittings the big brick building probably and the windows broken tiles missing and internal damage the steel frame blocks almost unharmed except for the windows interior partitions and fittings the factory the framework undamaged but the sheeting is still likely to be blown off it should be noted that with a bomb burst at a thousand feet there is no crater and no damage to public utility services below ground by blast itself but collapsing buildings may cause damage to such services the number of buildings destroyed and the resulting debris spread over an area of one-mile radius from Ground Zero will make rescue work extremely difficult so now let us examine the problem of accessibility from Ground Zero outwards for the first quarter of a mile all streets will be blocked with rubble varying from five to ten feet in depth depending on the construction of the buildings and the width of the roads these can only be cleared by heavy mechanical equipment we'll call this category a from a quarter mile to a half mile most streets will still be category a but some will be more easily cleared we'll call these category B from half a mile to three-quarters of a mile some streets will still be category a most will be category B but some will have less debris probably a profusion of tiles broken glass and lumps of masonry these would be open to traffic but only with difficulty and we'll call them category C from three-quarters of a mile to one mile most streets will be in category C but a number still in category B from one mile outwards worst streets will be open except for glass tiles and other light debris in all cases the amount of debris in the streets will depend on the direction of the blast in relation to the buildings as well as the type of construction of those buildings for instance in a case like this where the streets lined with brick buildings is at right angles to the direction of blast the debris may cover the whole street if they had been in line with the blast like this perhaps owned at the sides of the road would be vetted although a second road running at right angles would then be completely blocked in some cities that are broad highways leading right into the heart of the city these will never be completely blocked and will provide a means of access whatever the direction of blast if roads are severely blocked in all directions it should be remembered that waterways may provide a useful means of access within a quarter of a mile of Ground Zero bridges are likely to be destroyed and may be damaged up to half a mile away depending on their construction and the resulting debris might make navigation extremely difficult the same would apply to debris from buildings situated near narrow canals there are also special difficulties associated with access from tidal water as found in London in the last war the effect of blast from an our burst atomic bomb will inevitably cause widespread damage to the buildings of a city it will cause a large number of people to be trapped in their shelters a full knowledge by civil defence personnel of the effects of atomic blast and a proper understanding of the problems concerning accessibility to Ground Zero will prove to be a governing factor in the total casualty rate we have seen what the effects of an airburst atomic bomb heat radiation and blast might do to a typical British city let us now apply these effects to the population of that city and see what might happen to them in the first place if there had been no warning prior to the attack and then with the assumption that a clear five minute warning had been sounded we will assume that the attack is in daylight and the weather is fine except for the usual industrial haze that hangs over the city you remember that in measuring the effects of an atom bomb the point directly below the burst is known as ground zero we will now take a factory situated at a point a quarter of a mile away from Ground Zero it's nearly time for the shift to change over and the workers are hanging about outside nearby is the administrative block of modern steel girder construction at ground floor level is one of the secretaries standing near a window suddenly and without any warning an atomic bomb bursts 1,000 feet in the air and about a quarter of a mile away these people are all killed in theory they have died three times over firstly from heat flesh it would have killed them instantly and their bodies will be charred secondly they will have received a lethal dose of gamma rays and their bodies may be contaminated by fission products and thirdly they will be crushed under the debris and now the secretary now she is in an office on the far side of the block from the explosion she is shielded from the heat flash there are several floors above her and the thickness of another building at the back say three or four feet of concrete in all that should be sufficient to protect her from a lethal dose of gamma rays so she is protected from the first two effects that killed the workers out in the open but she will be killed by the effects of blast at a quarter of a mile from Ground Zero a modern steel framed block will be largely destroyed we will now put the clock back and assume that a warming has been sounded the workers go down into their shelter beneath the factory the secretary who is downstairs to the basement the workers are now fully protected from heat flash because they have two feet of concrete as a roof to their shelter they also have protection from radiation and from direct blast but being in a closely built-up area the debris from collapsed buildings as well as their own factory above them may possibly trap them in their shelter in spite of the special emergency exits provided the secretary in her basement has even better protection from heat and radiation than before blast will destroy the building but she will now have some chance of survival depending on how efficiently the basement has been reinforced she may be alive but she may also be prepped and like the others may require the services of the rescue party now let us take another group of people at a point to three-quarters of a mile away from Ground Zero and see what happens to them here is a street crossing in chef Ingham somewhere on the 3/4 mile circle mr. Smith is crossing the road notice that he wears a light-colored overcoat a hat and gloves the atom bomb explodes 3/4 of a mile away when he is just half way across in a fully exposed place mr. Smith is in a direct line with the explosion and will therefore receive all three effects from the bomb the heat flash would normally have killed him at this range but the industrial haze will lessen its power and mr. Smith's woolen coat affords him considerable protection his coat will be burnt and so may some of his clothes under it but he himself will stand a good chance of survival from the heat flash radiation at this range is still pretty powerful and he will more than likely receive a lethal dose although it may be a few days before the full effects become apparent but in any case blast will almost certainly kill him with an open street between him and the explosion the blast will be like a hurricane and will knock him down even though there's no building immediately in line to fall on him there will be a profusion of flying glass and pieces of masonry the people who had turned down this side street have the protection of the buildings against heat and radiation but parts of those same buildings would be pushed over on top of them and they would be killed by the effects of blast now if the people had received a warning they would have taken shelter mr. Smith would look about him for the solidly built building like this steel constructed store the people in the side street find the surface shelter handy and go into it mr. Smith is now protected from the effects that killed him namely radiation and blast he has full protection from heat his greatest danger would be from secondary blast although the building being steel-framed should not receive serious structural damage the false ceilings and partition walls may collapse also glass from windows and showcases would be a hazard it is likely that mr. Smith would be injured if he had time to go down to the basement shelter before the bomb exploded he would probably be unharmed the people in the surface shelter are again protected from heat and radiation and this time they will survive the blast effects the collapsing buildings may possibly block the shelter exit but its inhabitants will be alive and unharmed remember that at this distance rescue operations may well be hampered by serious fires now let's see what happens to mrs. Brown she lives in a semi-detached house at a point a mile and a half away from grounds her children have been evacuated and while mrs. Brown is waiting for her husband to come home she goes out into the yard to collect the washing off the line at a point a mile and a half away on the other side of the house - mrs. Brown the atomic bomb explodes without any prior warning the house acts as a shield from the heat flash at this range the gamma rays will not cause injury but the effect of blasts is still considerable although the house may not be destroyed by blast there will still be danger from falling chimney pots tiles and glass mrs. Brown will be very lucky if she escapes without some injury from one of these unless mrs. Brown had taken the precaution of whitewashing her windows there is a slight chance that the heat flash will have started a fire on the top floor front her injury may prevent her from dealing with the fire quickly and her house might then be gutted now if mrs. Brown had received a proper warning she would have gone to her Anderson shelter at this range of a mile and a half from Ground Zero she would then have been completely safe from all the effects of the atomic bomb she would be able to reenter her house and deal with any small fires as a final example let us look at mr. Jones he lives half a mile away a total of two miles from Ground Zero mr. Jones is just about to leave home and is standing in the doorway looking at the sky normally the brilliance of the heat flash would cause temporary blindness and would burn the exposed parts of his skin but in this case the industrial haze has reduced the brilliance and range of the flesh and he would probably only experience lights reddening of the skin and no other ill effects radiation at this range will be negligible but there may be a very slight risk from fission products in the fallout if he were downwind of the explosion the blast effect will break the windows of his house but it's unlikely to cause him any personal injury if there had been a warning and he had taken shelter he would be safe from any risk of injury in all the cases we have considered the people who are not sufficiently protected were killed or injured by one or more of the atomic bombs three effects when these same people were assumed to have taken proper cover in shelters or basements they stood a far better chance of not being killed by the effects of the bomb as in the last war the immediate first read problems are going to be those of rescue and firefighting only on a very much larger scale there will be the added problem of access through areas blocked by debris although the atomic bomb causes immense damage there is still a great deal that civil defense can do to save and protect life we can meet and defeat the atomic bomb attack as we have always met and defeated every attack against us but we can only do it by knowledge good organization good training good the planning and preparation beforehand [Music]