Editing Apollo 1 (section)

=== Major causes of accident ===
The review board identified several major factors which combined to cause the fire and the astronauts' deaths:<ref name="SP4029" />
* An ignition source most probably related to "vulnerable wiring carrying spacecraft power" and "vulnerable plumbing carrying a combustible and corrosive coolant"
* A pure oxygen atmosphere at higher than atmospheric pressure
* A cabin sealed with a hatch cover which could not be quickly removed at high pressure
* An extensive distribution of combustible materials in the cabin
* Inadequate emergency preparedness (rescue or medical assistance, and crew escape)

==== Ignition source ====
The review board determined that the electrical power momentarily failed at 23:30:55 GMT, and found evidence of several [[electric arc]]s in the interior equipment. They were unable to conclusively identify a single ignition source. They determined that the fire most likely started near the floor in the lower left section of the cabin, close to the Environmental Control Unit.<ref name="aibreport" />{{Reference page|page=6-1}} It spread from the left wall of the cabin to the right, with the floor being affected only briefly.<ref name="aibreport" />{{Reference page|page=5-3}}

The board noted that a silver-plated copper wire, running through an environmental control unit near the center couch, had become stripped of its [[Polytetrafluoroethylene|Teflon]] insulation and abraded by repeated opening and closing of a small access door.{{efn|In 1967 a vice president of North American Aviation, John McCarthy, speculated that Grissom had accidentally "scuffed the insulation of a wire" while moving about the spacecraft, but his remarks were ignored by the review board and strongly rejected by a congressional committee. [[Frank Borman]], who had been the first astronaut to go inside the burned spacecraft, testified, "We found no evidence to support the thesis that Gus, or any of the crew members kicked the wire that ignited the flammables." A 1978 history of the accident written internally by NASA said at the time, "This theory that a scuffed wire caused the spark that led to the fire still has wide currency at Kennedy Space Center. Men differ, however, on the cause of the scuff."<ref name = spaceport>{{Cite book |last1=Benson |first1=Charles D. |url=http://www.hq.nasa.gov/office/pao/History/SP-4204/ch18-6.html |title=Chapter 18-6 – The Fire That Seared The Spaceport, "The Review Board" |last2=Faherty |first2=William Barnaby |publisher=NASA |year=1978 |series=NASA History Series |lccn=77029118 |id=NASA SP-4204 |ref=moonport |access-date=August 5, 2020}}</ref> Soon after making his comment McCarthy had said, "I only brought it up as a hypothesis."<ref>{{Cite magazine |date=April 21, 1967 |title=Blind Spot |magazine=[[Time (magazine)|Time]] |url=http://www.time.com/time/magazine/article/0,9171,843575-2,00.html |archive-url=https://web.archive.org/web/20090114084112/http://www.time.com/time/magazine/article/0,9171,843575-2,00.html |archive-date=January 14, 2009 |access-date=May 21, 2008}}</ref>}}

This weak point in the wiring also ran near a junction in an [[ethylene glycol]]/water cooling line that had been prone to leaks. [[Electrolysis]] of ethylene glycol solution with the silver [[anode]] of the wire was discovered at the [[Manned Spacecraft Center]] on May 29, 1967, to be a hazard capable of causing a violent [[exothermic reaction]], igniting the ethylene glycol mixture in the Command Module's pure oxygen atmosphere. Experiments at the [[Illinois Institute of Technology]] confirmed the hazard existed for silver-plated wires, but not for copper-only or nickel-plated copper. In July, ASPO directed both North American and Grumman to ensure no silver or silver-coated electrical contacts existed in the vicinity of possible glycol spills in the Apollo spacecraft.<ref>{{Cite book |last1=Ertel |first1=Ivan D. |url=http://www.hq.nasa.gov/office/pao/History/SP-4009/contents.htm#Volume%20IV |title=The Apollo Spacecraft: A Chronology |last2=Newkirk |first2=Roland W. |last3=Brooks |first3=Courtney G. |publisher=NASA |year=1969–1978 |volume=IV |location=Washington, D.C. |chapter=Part 2 (B): Recovery, Spacecraft Redefinition, and First Manned Apollo Flight: May 29, 1967 |lccn=69060008 |oclc=23818 |id=NASA SP-4009 |display-authors=2 |access-date=July 12, 2013 |chapter-url=http://www.hq.nasa.gov/office/pao/History/SP-4009/v4p2b.htm |archive-date=February 5, 2008 |archive-url=https://web.archive.org/web/20080205020128/http://www.hq.nasa.gov/office/pao/History/SP-4009/contents.htm#Volume%20IV |url-status=dead }}</ref>

==== Pure oxygen atmosphere ====

The plugs-out test had been run to simulate the launch procedure, with the cabin pressurized with pure oxygen at the nominal launch level of {{convert|16.7|psi|kPa|abbr=on}}, {{convert|2|psi|kPa|abbr=on}} above standard sea level atmospheric pressure. This is more than five times the {{convert|3|psi|kPa|abbr=on}} partial pressure of oxygen in the atmosphere, and provides an environment in which materials not normally considered flammable will be highly flammable and burst into flame.<ref>{{Cite web |last=Benson |first=Charles D. |last2=Faherty |first2=William Barnaby |title=Moonport, CH18-2 |url=http://www.hq.nasa.gov/office/pao/History/SP-4204/ch18-2.html |url-status=dead |archive-url=https://web.archive.org/web/20160325215950/http://www.hq.nasa.gov/office/pao/History/SP-4204/ch18-2.html |archive-date=March 25, 2016 |access-date= |website=www.hq.nasa.gov}}</ref><ref name="SpaceSafetyMag">{{Cite magazine |last=Emmanuelli |first=Matteo |title=The Apollo 1 Fire |url=http://www.spacesafetymagazine.com/space-disasters/apollo-1-fire/ |magazine=Space Safety Magazine |year=2014 |access-date=April 14, 2016}}</ref>

The high-pressure oxygen atmosphere was similar to that which had been used successfully in the [[Project Mercury|Mercury]] and Gemini programs. The pressure before launch was deliberately greater than ambient in order to drive out the nitrogen-containing air and replace it with pure oxygen, and also to seal the [[plug door]] hatch cover. During the launch, the pressure would have been gradually reduced to the in-flight level of {{convert|5|psi|kPa|abbr=on}}, providing sufficient oxygen for the astronauts to breathe while reducing the fire risk. The Apollo{{nbsp}}1 crew had successfully tested this procedure with their spacecraft in the Operations and Checkout Building altitude (vacuum) chamber on October 18 and 19, 1966, and the backup crew of Schirra, Eisele and Cunningham had repeated it on December 30.<ref>[[#moonport|Benson 1978]]: [http://www.hq.nasa.gov/office/pao/History/SP-4204/ch18-3.html Chapter 18-3 – The Spacecraft Comes to KSC] {{Webarchive|url=https://web.archive.org/web/20140803002233/http://www.hq.nasa.gov/office/pao/History/SP-4204/ch18-3.html |date=August 3, 2014 }}</ref> The investigation board noted that, during these tests, the command module had been fully pressurized with pure oxygen four times, for a total of six hours and fifteen minutes, two and a half hours longer than it had been during the plugs-out test.<ref name="aibreport" />{{Reference page|page=4-2}}{{efn|The report mistakenly says "about {{frac|2|1|2}} times longer", which is clearly incorrect because the cabin had been pressurized for about {{frac|3|3|4}} hours during the plugs-out test.}}

==== Flammable materials in the cabin ====
The review board cited "many types and classes of combustible material" close to ignition sources. The NASA crew systems department had installed {{convert|34|sqft|m2}} of [[Hook-and-loop fastener|Velcro]] throughout the spacecraft, almost like carpeting. This Velcro was found to be flammable in a high-pressure 100% oxygen environment.<ref name="SpaceSafetyMag" /> Astronaut [[Buzz Aldrin]] states in his book ''Men From Earth'' that the flammable material had been removed per the crew's August 19 complaints and Joseph Shea's order, but was replaced before the August 26 delivery to Cape Kennedy.<ref>{{Cite book |last1=Aldrin |first1=Buzz |title=Men From Earth |last2=McConnell |first2=Malcolm |date=1989 |publisher=Bantam Books |location=New York |page=178 |isbn=978-0-553-05374-6}}</ref>

==== Hatch design ====
[[File:AS-204 - hatch.jpg|thumb|The Block{{nbsp}}I hatch, as used on Apollo{{nbsp}}1, consisted of two pieces, and required pressure inside the cabin to be no greater than atmospheric in order to open. A third outer layer, the boost protective hatch cover, is not shown.]]

The inner hatch cover used a [[plug door]] design, sealed by higher pressure inside the cabin than outside. The normal pressure level used for launch ({{convert|2|psi|kPa|abbr=on}} above ambient) created sufficient force to prevent removing the cover until the excess pressure was vented. Emergency procedure called for Grissom to open the cabin vent valve first, allowing White to remove the cover,<ref name="SP4029" /> but Grissom was prevented from doing this because the valve was located to the left, behind the initial wall of flames. Also, while the system could easily vent the normal pressure, its flow capacity was utterly incapable of handling the rapid increase to {{convert|29|psi|kPa|abbr=on}} caused by the intense heat of the fire.<ref name="aibreport" />{{Reference page|page=5-3}}

North American had originally suggested the hatch open outward and use [[explosive bolt]]s to blow the hatch in case of emergency, as had been done in [[Project Mercury]]. NASA did not agree, arguing the hatch could accidentally open, as it had on Grissom's ''[[Mercury-Redstone 4#Liberty Bell 7|Liberty Bell 7]]'' flight, so the [[Lyndon B. Johnson Space Center|Manned Spacecraft Center]] designers rejected the explosive design in favor of a mechanically operated one for the Gemini and Apollo programs.<ref name= "chariots9-2">{{Cite book |last1=Brooks |first1=Courtney G. |url=https://history.nasa.gov/SP-4205/cover.html |title=Chariots for Apollo: A History of Manned Lunar Spacecraft |last2=Grimwood |first2=James M. |last3=Swenson |first3=Loyd S. Jr. |publisher=Scientific and Technical Information Branch, NASA |others=Foreword by [[Samuel C. Phillips]] |year=1979 |isbn=0-486-46756-2 |series=NASA History Series |location=Washington, DC |chapter=Stalked by the Spectre |oclc=4664449 |id=NASA SP-4205 |access-date= January 6, 2016 |chapter-url=http://www.hq.nasa.gov/office/pao/History/SP-4205/ch9-2.html}}</ref> Before the fire, the Apollo astronauts had recommended changing the design to an outward-opening hatch, and this was already slated for inclusion in the Block II command module design. According to [[Deke Slayton|Donald K. Slayton]]'s testimony before the House investigation of the accident, this was based on ease of exit for spacewalks and at the end of flight, rather than for emergency exit.<ref name = spaceport/>

==== Emergency preparedness ====
The board noted that the test planners had failed to identify the test as hazardous; emergency equipment (such as gas masks) were inadequate to handle this type of fire; that fire, rescue, and medical teams were not in attendance; and that the spacecraft work and access areas contained many hindrances to emergency response such as steps, sliding doors, and sharp turns.<ref name="aibreport" />{{Reference page|page=6-1, 6-2}}