14 April 1967, the dam was reinforced by an explosion of 3,900 tonnes of ammonium nitrate-based explosive. CHASE 5, off Puget Sound On 23 May 1966, Izaac Van Zandt was loaded with of obsolete munitions containing of high explosives. The cargo was detonated off Puget Sound at a depth of . CHASE 6, off New Jersey On 28 July 1966, Horace Greeley was loaded with obsolete munitions and detonated off New Jersey at a depth of . N1 launch explosion On 3 July 1969, an N1 rocket in the Soviet Union exploded on the launch pad of Baikonur Cosmodrome, after a turbopump exploded in one of the engines. The entire rocket contained about of kerosene and of liquid oxygen. Using a standard energy release of 43 MJ/kg of kerosene gives about 29 TJ for the energy of the explosion (about 6.93 kt TNT equivalent). Investigators later determined that up to 85% of the fuel in the rocket did not detonate, meaning that the blast yield was likely no more than 1 kt TNT equivalent. Comparing explosions of initially unmixed fuels is difficult (being part detonation and part deflagration). Old Reliable Mine Blast On 9 March 1972, 2,000 tons (4 million pounds) of explosive were detonated inside three levels of tunnels in the Old Reliable Mine near Mammoth, Arizona. The blast was an experimental attempt to break up the ore body so that metals (primarily copper) could be extracted using sulfuric acid in a heap-leach process. The benefits of increased production were short-lived while the costs of managing acid mine drainage due to the sulfide ore body being exposed to oxygen continue to the present day. Flixborough disaster On 1 June 1974, a pipe failure at the Nypro chemical plant in Flixborough, England, caused a large release of flammable cyclohexane vapour. This ignited and the resulting fuel-air explosion destroyed the plant, killing 28 people and injuring 36 more. Beyond the plant 1,821 houses and 167 shops and factories had suffered to a greater or lesser degree. Fires burned for 16 days. The explosion occurred at a weekend otherwise the casualties would have been much heavier. This explosion caused a significant strengthening of safety regulations for chemical plants in the United Kingdom. Iri station explosion On 11 November 1977, a freight train carrying 40 tons of dynamite from Gwangju suddenly exploded at Iri station (present-day Iksan), Jeollabuk-do province, South Korea. The cause