What is a safe radiation dose?

Mumbai: In the wake of crisis at Fukushima nuclear plant in tsunami-hit Japan, 'safe radiation dose' is one of the terms that is being repeatedly used by pundits. 

Safe radiation dose is the amount of radiation that humans can be exposed to without getting harmed.

Former Secretary of Atomic Energy Regulatory Board, and an expert on radiation protection, Dr K S Parthasarathy said that as per the Board, the annual dose for radiation workers (working at the reactor site) should be "as low as reasonably achievable" (ALARA). 

"It should not exceed 30 millisievert (mSv) excluding the dose due to natural background radiation and medical exposure, if any," Parthasarathy told PTI today . 

"AERB dose limit at 30mSv is lower than 50 mSv prescribed by USA " he said. 

"I myself had received about 0.9mSv while recovering a lost radiation source used in industry," he said. 

"During the Fukushima nuclear emergency procedures (currently) one worker received 106mSv. Dose to the recovery workers are not published so far," he said. 

For ordinary members of the public, the dose limit is one mSv. In the case of pregnant women, the dose to the foetus should not exceed one mSv.

"During medical procedures (where radiation may be used) the following doses in mSv may be considered as safe. Cardiac CT scan 12; angioplasty on an average 400 and at times even 1000mSv; treatment of hyperthyroidism, 100,000; radiation treatment of cancer 60,000 mSv to the part of the body...In USA, the dose limit for an astronaut is 250mSv per mission. 

"Thus, we accept different values of doses as safe and acceptable, depending on circumstances. One need not lose sleep over receiving a few tens of mSv, if the occasion demands it," he added.