MIKUNI, Fukui Pref. -- Five volunteers helping to clean up the oil spill on the Sea of Japan coast have died of either a heart attack or stroke, prompting the largest citizens' headquarters coordinating the operations to place increased emphasis on safety.

"From day one, our biggest fear was that volunteers would get caught up in an accident, swept away by waves or something. Preventing that was more of a priority than cleaning the spill," said Kouji Yagi, a spokesman for the volunteer organizers based here.

The deaths, however, were not by drowning. Over-eager, often elderly volunteers have succumbed to either a heart attack or stroke. None of the victims had been working for the organization, which has now introduced measures to save volunteers from themselves, Yagi said.

"If you feel bad, leave the oil spill area immediately, then inform your team leader. Take a break whenever you want. You're the best judge of your own body's condition, so don't wait for instructions on this," an organizer shouted at a briefing for volunteers here last Feb. 2.

So far, about 15,000 volunteers have visited the headquarters on the shore near the grounded bow section of the Russian oil tanker Nakhodka. Only after new volunteers have registered for insurance, completed a health check, been issued a face mask and written their blood type on their name cards are they briefly told how to clean up the oil. "The deaths have occurred because people who were prone to a heart attack worked out in the cold for hours. When older people or those with high blood pressure come in, we ask them to do less strenuous work around the headquarters, even if this means disappointing them," said Dr. Yasuo Nameda of Kinki University, who is working at the headquarters.