exposed pipe surfaces with asbestos drop cloths (required to protect piping systems from accidental exposure to welding sparks), due to the cramped working space. A drop from a welding electrode fell on an unprotected surface, producing an invisible crack. This crack was subject to prolonged and intensive pressure (over 200 atmospheres), compromising the pipe's integrity and finally causing it to fail. Others disputed this conclusion. Retired Rear-Admiral Nikolai Mormul asserted that when the reactor was first started ashore, the construction crew had not attached a pressure gauge to the primary cooling circuit. Before anyone realized there was a problem, the cooling pipes were subjected to a pressure of 400 atmospheres, double the acceptable limit. On 1 February 2006, former President of the Soviet Union Mikhail Gorbachev proposed in a letter to the Norwegian Nobel Committee that the crew of K-19 be nominated for a Nobel Peace Prize for their actions on 4 July 1961. Deceased crew members Several crew members received fatal doses of radiation during repairs on the reserve coolant system of Reactor #8. Eight died between one and three weeks after the accident from severe radiation sickness. A person who receives a dose of 4 to 5 Sv (about 400-500 rem) over a short period has a 50% chance of dying within 30 days. Fourteen other crew members died within two years. Many other crew members also received radiation doses exceeding permissible levels. They underwent medical treatment during the following year. Many others experienced chest pains, numbness, cancer, and kidney failure. Their treatment was devised by Professor Z. Volynskiy and included bone marrow transplantation and blood transfusion. It saved, among others, Chief Lieutenant Mikhail Krasichkov and Captain 3rd class Vladimir Yenin, who had received doses of radiation that were otherwise considered deadly. For reasons of secrecy, the official diagnosis was not "radiation sickness" but "astheno-vegetative syndrome", a mental disorder. Crew members decorated On 6 August 1961, 26 members of the crew were decorated for courage and valor shown during the accident. Later operational history On 14 December 1961, the boat was fully upgraded to the Hotel II (658м) variant, which included upgrading to R-21 missiles, which had twice the effective range of the earlier missiles. Collision At 07:13 on 15 November 1969, K-19 collided with the attack submarine in the Barents Sea at a depth of . She was able to surface using an emergency main ballast tank