A guiding principle of<unk>  safety is as low as reasonably achievable (ALARA). This means try to avoid exposure as much as possible and includes the three components of time, distance, and shielding. Time The longer that humans are subjected to<unk>  the larger the dose will be. The advice in the nuclear war manual entitled Nuclear War Survival Skills published by Cresson Kearny in the U.S. was that if one needed to leave the shelter then this should be done as rapidly as possible to minimize exposure. In chapter 12, he states that "quickly putting or dumping wastes outside is not hazardous once fallout is no longer being deposited. For example, assume the shelter is in an area of heavy fallout and the dose rate outside is 400 roentgen (R) per hour, enough to give a potentially fatal dose in about an hour to a person exposed in the open. If a person needs to be exposed for only 10 seconds to dump a bucket, in this 1/360 of an hour he will receive a dose of only about 1 R. Under war conditions, an additional 1-R dose is of little concern." In peacetime,<unk>  workers are taught to work as quickly as possible when performing a task that exposes them to<unk> . For instance, the recovery of a radioactive source should be done as quickly as possible. Shielding Matter attenuates<unk>  in most cases, so placing any mass (e.g., lead, dirt, sandbags, vehicles, water, even air) between humans and the source will reduce the<unk>  dose. This is not always the case, however; care should be taken when constructing shielding for a specific purpose. For example, although high atomic number materials are very effective in shielding photons, using them to shield beta particles may cause higher<unk>  exposure due to the production of bremsstrahlung x-rays, and hence low atomic number materials are recommended. Also, using material with a high neutron activation cross section to shield neutrons will result in the shielding material itself becoming radioactive and hence more dangerous than if it were not present. There are many types of shielding strategies that can be used to reduce the effects of<unk>  exposure. Internal contamination protective equipment such as respirators are used to prevent internal deposition as a result of inhalation and ingestion of radioactive material. Dermal protective equipment, which protects against external contamination, provides shielding to prevent radioactive material from being deposited on external structures. While these protective measures do provide a barrier from radioactive material deposition, they do not shield from externally penetrating gamma<unk> . This leaves anyone exposed to penetrating gamma rays at high risk of<unk> . Naturally, shielding the entire body from high energy gamma<unk>  is optimal, but the required mass to provide adequate attenuation makes functional movement nearly impossible. In the event of a<unk>  catastrophe, medical and security personnel need mobile protection equipment in order to safely assist in containment, evacuation, and many other necessary public safety objectives. Research has been done exploring the feasibility of partial body shielding, a<unk>  protection strategy that provides adequate attenuation to only the most radio-sensitive organs and tissues inside the body. Irreversible stem cell damage in the bone marrow is the first life-threatening effect of intense<unk>  exposure and therefore one of the most important bodily elements to protect. Due to the regenerative property of hematopoietic stem cells, it is only necessary to protect enough bone marrow to repopulate the exposed areas of the body with the shielded supply. This concept allows for the development of lightweight mobile<unk>  protection equipment, which provides adequate protection, deferring the onset of<unk>  to much higher exposure doses. One example of such equipment is the 360 gamma, a<unk>  protection belt that applies selective shielding to protect the bone marrow stored in the pelvic area as well as other radio sensitive organs in the abdominal region without hindering functional mobility. More information on bone marrow shielding can be found in the article , or in the Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency (NEA)'s 2015 report: Reduction of incorporation Where radioactive contamination is present, an elastomeric respirator, dust mask, or good hygiene practices may offer protection, depending on the nature of the contaminant. Potassium iodide (KI) tablets can reduce the risk of cancer in some situations due to slower uptake of ambient radioiodine. Although this does not protect any organ other than the thyroid gland, their effectiveness is still highly dependent on the time of ingestion, which would protect the gland for the duration of a twenty-four-hour period. They do not prevent<unk>  as they provide no shielding from other environmental radionuclides. Fractionation of dose If an intentional dose is broken up into a number of smaller doses, with time allowed for recovery between irradiations, the same total dose causes less cell death. Even without interruptions, a reduction in dose rate below 0.1 Gy/h also tends to reduce cell death. This technique is routinely used in radiotherapy. The human body contains many types of cells and a human can be killed by the loss of a single type of cells in a vital organ. For many short term<unk>  deaths (3–30 days), the loss of two important types of cells that are constantly being regenerated causes death. The loss of cells forming blood cells (bone marrow) and the cells in the digestive system (microvilli, which form part of the wall of the intestines) is fatal.
Acute radiation syndrome
Chronic radiation syndrome
Second-impact syndrome
Majeed syndrome
FACES syndrome
Post-intensive care syndrome
Post-polio syndrome
Decompression sickness