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Japan Update

On March 11 a major earthquake and tsunami caused widespread destruction primarily in northeastern Japan, with aftershocks continuing, including in Tokyo which is further south. There is an exclusion zone surrounding the Fukushima Daiichi nuclear plant located in northeastern Japan south of Miyagi Prefecture (see additional information below).

Health recommendations for most areas of the country align with the normal indications for Japan at this time of year. It is end of winter with overnight temperatures near freezing, especially in the north. Insects do not pose a problem, and warm clothing and shelter are important for relief workers.

Other recommendations for rescue and relief workers to areas of devastation include vaccination against hepatitis A, hepatitis B, and influenza, plus all routine vaccines (tetanus in particular must be up-to-date, and measles is indicated for all unvaccinated health care workers without other evidence of immunity). Hepatitis B requires that a series be completed; a single dose is not protective. The risk of traveler’s diarrhea in Japan is usually minimal; however, due to potential disaster-related water contamination, travelers should practice diligent food- and beverage-precautions and carry loperamide and a quinolone antibiotic for presumptive self-treatment.

Adequate first aid supplies should be carried in order to treat skin infections. Sturdy shoes are important due to widespread debris. Japan is rabies free in terrestrial animals.

The Japanese Atomic Energy Agency has classified the ongoing events at nuclear reactors in Japan as a consequence of the recent earthquake and subsequent tsunami as an International Nuclear Event Scale level 4 event:

“Nuclear accident with local consequences.” For reference, Three Mile Island was a 5 and Chernobyl was a 7 (on a 7 point scale). This rating is based on the fact that there has been no evidence of primary containment structure rupture, but there has been detection of fission by-products cesium and iodine with moderately elevated levels of radiation in the immediate vicinity area of the reactor complex, and known controlled release of low-level radioactive vapors (as authorities attempt to control pressure and temperature in the reactor vessels).

 The prevailing winds in the area are seaward, so the threat to populated areas from current conditions are minimal, although the situation is not stabilized. Military vessels in the area have reported low levels of radiactive particulate matter that is effectively managed by exiting downwind areas and washing down the affected areas.

Readers should pay close attention to terminology used to describe events.

While there has been an “explosion” at a reactor site (and reports of conditions buiding that could lead to a second similar explosion), there has been no breach of primary containment structures at reactors, so the sources of high volume, high level radioactivity are fully contained. Explosions that have occured have been non-nuclear, primarily caused by excessive concentrations of non-radioactive hydrogen gas in structures surrounding reactors.

 There may or may not have been a partial melting of fuel rods in reactors, but there is no evidence of a “core meltdown” or extensive melting of fuel rods. Importantly, all reports indicate that control rods (the devices that absorb nuclear particles, thus modulating the nuclear reaction), are all fully inserted, so that sustained reaction cannot continue, although residual heat in the fuel rods, thus the importance of continued cooling, continues to be a signficant event management concern.

 The greatest current concern is ongoing reports of difficulty in maintaining adequate volumes of coolant in both containment structures and fuel rod storage areas. This increases the risk of further melting of nuclear fuel, but, especially because of the presence of the control rods and the addition of other nuclear particle absorbers (e.g., boric acid), there is essentially no risk of sustained reaction. The inability to adequately control heat, however, could result in additional controlled or uncontrolled venting of gases with radioactivity, which would continue to follow low-level prevailing wind patterns, with primary dispersion to sea.

Potassium Iodide is used for reducing uptake by the body of radioactive cesium or potassium. For there to be enough iodine or cesium in the atmosphere for this to be useful, there would most likely have to be rupture of the containment vessel. This is an exceedingly low-liklihood occurence.

Current recommendations (does not apply to responders to the event, who should follow guidance from appropriate authorites): No prophylaxis is needed.  Vessels (air and water) should avoid transitting downwind areas and should ideally monitor for radioactive particulates and use simple washing if any radioactivity is noted. In the absence of monitoring capability, washing of structures and personnel after transit is prudent. Personnel should continue to monitor news reports with special attention to reports of increased or uncontrolled venting of gases from containment structures and for changes in wind patterns that could direct venting to populated areas.

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