Editing Piper Alpha (section)

===Subsequent gas pipeline ruptures and platform collapse===
At 22:20, in a case of [[Domino effect accident|domino effect]],{{sfnp|Mannan|2012|p=340|}} the heat from the burning oil collecting on the diving platform caused the nearby Tartan pipeline to rupture violently.{{sfnp|The Hon Lord Cullen|1990| loc=vol. 1, p. 43}} This discharged enormous amounts of highly flammable gas (some 30&nbsp;tonnes only in the first minute of the release),<ref name=":18" /> which immediately ignited into a massive [[jet fire]].<ref name=":17" />{{sfnp|Mannan|2012| p=1276|}} The heat and vibrations of the fire were felt by the crews in vessels as far away as {{Convert|1|km|mi}} from the rig. From that moment on, the platform's destruction was inevitable.<ref name=":14" /> This potential for an extreme escalation scenario was known to Occidental; a report commissioned by them in 1986 stated{{sfnp|McGinty|2009| pp=55–56|}} that the gas pipelines "would take hours to depressurize because of their capacity. This could result in a high pressure gas fire on the cellar deck that would be virtually impossible to fight, and the protection systems would not be effective in providing the cooling needed for the duration of the depressurisation".

The MCP-01 pipeline failed at 22:50 as a result of domino effect, and the ensuing jet fire{{sfnp |Mannan|2012|p=1276}} shot huge flames over {{convert|300|ft|m|-1|abbr=on}} into the air.<ref name=":14" /> At this time, around 187 men had not evacuated; however, many of them had already perished.<ref name=":5">{{Cite news |date=6 July 2013 |title=Piper Alpha: How We Survived North Sea Disaster |url=https://www.bbc.com/news/uk-scotland-22840445 |url-status=live |archive-url=https://web.archive.org/web/20231214114752/https://www.bbc.com/news/uk-scotland-22840445 |archive-date=14 December 2023 |access-date=1 April 2025 |work=[[BBC News]] |language=}}</ref> Personnel still left alive were either desperately sheltering in the scorched, smoke-filled accommodation block or leaping from the various deck levels, including the helideck, {{convert|175|ft|m||abbr=on}} into the North Sea.<ref name=":36">{{Cite episode |title=Oil Rig Explosion |series=Make It Out Alive! |network=[[Smithsonian Channel]] |date=5 November 2017 |season=1 |number=4 |last=Keane |first=Garry}}</ref>

The Claymore gas line ruptured at 23:20, adding even more fuel to the already massive jet fires on board Piper Alpha.{{sfnp|The Hon Lord Cullen|1990|loc=vol. 1, p. 44}} At this point the Claymore OIM had received orders from Aberdeen to shut down production, and the gas flowline to Piper with it. He had initiated a pipeline blowdown (depressurization) but this was not yet complete at the moment of the rupture. Tartan's gas pipeline had been shut down around 22:30, with its blowdown commencing around 23:20.{{sfnp|Matsen|2011|loc=chapter 15}}{{sfnp|The Hon Lord Cullen|1990|loc=vol. 1, pp. 140–141}}{{Efn|Although the isolation and blowdown of the Claymore and Tartan gas pipelines occurred so late, it is unlikely that prompter action would have changed the fate of the disaster. In fact, the inventory and pressure in the pipelines were too high and depressurization would have taken too long even if it had started immediately.{{sfnp|The Hon Lord Cullen|1990|loc=vol. 1, p. 144}}{{sfnp|Spouge|1999|loc=appendix III, p. 8}} However, a quicker action to shut down oil production may have had some positive effect in delaying the failure of the Tartan riser (the conflagration occurred at 22:20 that doomed Piper),{{sfnp|The Hon Lord Cullen|1990|loc=vol. 1, pp. 143–144}} because the main oil pipeline shutdown valve on Piper was leaking, thus allowing a backflow of oil into the fire.{{sfnp|Mannan|2012|p=683}}}}

Around 23:45, with critical support structures failing from the intense heat, the platform began to collapse. One of the cranes fell first, followed by the drilling derrick. The generation and utilities module (D) and the fireproofed accommodation block, still occupied by crewmen who had sheltered there, then slipped into the North Sea.<ref name="pate" /> Some 80 men were in the block at the time.<ref name=":5" /> By 00:45, 7 July, almost all of Piper Alpha was gone, with only module A still standing.<ref name=":17" />