hazards existing at the moment of actual explosion. On the other hand, personnel injuries caused by over~exposure to the persistent radiol-:gical hazards produced as a result of the detonation can very often be either prevented or mitigated through detection and avoidance of those hazards, In view of these facts, the detection and avoidance of radiological hazards necessarily becomes the basic principle for all radiological defense operations within the civil defense progran, External and Internal Radiation Hazards. One highly insidious characteristic of many radiological hazards is the fact that they may exist either outside of or within the human body. In most instances, the source of radiation Temains outside the body and causes injury through penetration of the tissues from without. Under these circumstances, the rays or particles are termed external radiations, Broadly speaking, injuries attributable to this type of hazard usually become apparent within three weeks after exposure, Qn the other hand, radioactive fission products, or “bomb waste", may inadvertently enter the dody, This usually takes place by direct methods, such as inhalation or contaminatiom of open cuts or womnds, It may, however, occur indirectly, as is the case when humans eat fishes whose bodies contain radioactive materials picked up in feeding, Once inside the body, the radiations from such materials penetrate and ionize the tissues from within and are consequently called internal hazards, Since the amount of material entering the body is usually small and its radioactive intensity comparatively low but of ten longlived, injuries attributable to internal hazards may not become apparent for several years, Limitations of Protective Clothing and Devices. Insofar as highly intensive radiations sre concerned, truly vrotective clothing is non-existent and there DO® ARCHIVES