In addition to the safety efforts usually employed in atomic test operations, considerable forethought and planning were required in the handling of liquified hydrogen. The Ivy operation overseas and its preparation in the ZI involved the handling of liquified hydrogen in quantities not previously encountered. The safety aspects of engineering design and operating procedures were continuously reviewed by LASL personnel who retained as safety consultants recognized Jeaders in the commercial field. In the development of experience with this product a conservative approach was adopted. Standard safety techniques for combustible gases were used and modified as experience and circumstances indicated. Although liquified hydrogen is recognized as the most energetic chemical fuel, it has desirable properties that facilitate simple safety techniques. For example, although the mixtures of hydrogen gas and air do have a wide explosive range, they re- quire a relatively high concentration of hydrogen as a lower explosive limit, which means that, compared to most other combustible gases, a larger quantity of hydrogen must be free for a risk to be present. In addition, although liquid hydrogen has a low heat of vaporization, it also has a high rate of diffusion and thus is easily dissipated. Both these characteristics, a high lower explosive limit and a rapid upward diffusion rate, make the problems of safe handling not too difficult. Adequate ventilation was readily incorporated in the designs and operating procedures so that the prevailing conditions were continuously safe, with minimum risk even in the case of untoward incidents. These safety features were incorporated for all operations of TU 2, 3, and 4. The primary roll-up of equipment for TU 3 was completed prior to Mike Shot. Virtually all equipment, except three Dewars and several “transportainers,” was ready for evacuation by M-—3 days. This left only a very small amount of equipment and materials to be handled after Mike Shot. The over-all storage efficiency of the TU 3 Dewars, from the time of receiving liquid . hydrogen until itwas emptied from the Dewars, and including all losses of every kind (from normal heat leaks, from accidents, from Dewar-to-Dewar transfers, from some experiments, and from malfunction of the equipment) was 95 per cent over a period of approximately 2! months. Since the one completely critical commodity, for which TU 3 was responsible, was deuterium, it is interesting to note that, of stored by TU 3 over a period of 36 days, the total loss was 0 liters. 4.4 TASK UNIT 4, MIKE ASSEMBLY TU 4 was organized to prepare for shipment and to assemble the complete Mike device. CTU 4 coordinated the Mike assembly at all points for all groups and contractors. These groups consisted of personnel of American Car and Foundry (ACF) and CMR, GMX, and W Divisions, LASL. Each of these groups was responsible for various specific assembly operations. For example, ACF was responsible for the mechanical assembly of the device; CMR was responsible for the cryogenics system, and W-1 was responsible for all nuclear components. Prior to the assumpcion by CTG 132.1 of operational control of the device, TU 4 maintained efficient liaison with all the diversified groups of the Laboratory concerned with the development of the Mike device. The Mike device was shipped to Eniwetok aboard the USS Curtiss, and after the arrival of TU 4 personnel in the Forward Area in mid-September the Mike assembly program began with the components being unloaded as necessary from the USS Curtias to the cab on Elugelab Island. Prior to departure for the Forward Area, a schedule of operations for assembly of the device, and for other installation within the cab after commencement of the device assembly, was decided upon. This schedule took into account not only the predicted assembly time of the 57