If your life is in danger, call the police at 110

全国社会福祉協議会(Zenkoku shakai fukushi Kyogikai)

This organisation provides insurance for people taking part in volunteer activities, such as in disaster areas. It is first necessary to register with them which is done via the nearest office (https://www.fukushihoken.co.jp/fukushi/front/council/volunteer_activities.html)
03-3581-4656 (全国ボランティア・市民活動振興センター)