From a Scientific American article$^\color{magenta}{\star}$ on an ammonia leak at the ISS:

Ammonia is so toxic that spacewalks nearby the substance must have extra precautions built in to reduce exposure risk to astronauts

What are these “extra precautions”? I can’t imagine how an EVA suit could be improved upon for protection during the EVA. Are they referring to the other ISS staff being exposed after the EVA astronaut has cleared the airlock?

For now, NASA has asked its Expedition 70 ISS astronauts to close all shutters on the U.S. segment of the space station "as a precaution against contamination," agency officials wrote.

What "shutters" are these?

$\color{magenta}{\star}$ Elizabeth Howell, International Space Station suffers leak, but crew remains safe, Space.com, October 11, 2023.


1 Answer 1


"extra precautions" = visual inspections and bakeout time.

The entire “Wet QD” ops was timelined in order to allow enough time for a “bake out” prior to ingress, should the EMUs become contaminated with any leaking ammonia from the QDs.

  • EMU = Extravehicular Mobility Unit aka spacesuit
  • QD = Quick Disconnect

From https://www.nasaspaceflight.com/2012/11/astronaut-duo-spacewalk-iss-isolate-ammonia-leak/

Another example

We know there is ammonia in the area... so they will do a visual inspection of each other to make sure there is no ammonia ice on their suits. Once they have concluded that they are clean, that starts a bake out timer. We do that to make sure we have adequate time for any hidden ammonia that might be on the suits to evaporate. On a rough order of magnitude, 30 to 45 minutes is required for that bake out time.

That clock starts and they will begin their transit back to the airlock, down the P6 truss. Once they get in the airlock, they will hook up on umbilicals, they will repress the airlock to 5 psi and perform a test... a simple way of detecting of how much ammonia might be in the atmosphere at that 5 psi level. And based on that we'll make a determination if there is contamination or not. If consumables permit, they may do a second test. We don't anticipate that to be required.

ISS Flight Director Norm Knight quoted here http://www.collectspace.com/ubb/Forum30/HTML/001202.html

"What "shutters" are these?"

The ISS windows (at least on the US side) have external shutters most easily seen on the cupola.

enter image description here

From https://images-assets.nasa.gov/image/iss023e042367/iss023e042367~orig.jpg, hand-drawn circles mine.

This image from STS-130 shows all the cupola shutters closed

enter image description here

(Image: NASA)

  • $\begingroup$ Thanks. I had pictured "shutters" as being Venetian Blinds. Is the "bake-out time" done after pressurizing the airlock? $\endgroup$
    – Woody
    Dec 10, 2023 at 2:10
  • $\begingroup$ So the "extra protection" is AFTER, not DURING the EVA? $\endgroup$
    – Woody
    Dec 10, 2023 at 2:11
  • $\begingroup$ @Woody Inspection & bakeout is prior to airlock ingress. They can be moving during bakeout. Added more of the FD quote. $\endgroup$ Dec 10, 2023 at 2:13
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    $\begingroup$ FWIW, ammonia can be neutralised (kind of) by reacting it with chlorine, producing ammonium chloride. But I suppose chlorine-based bleach isn't popular on the ISS... $\endgroup$
    – PM 2Ring
    Dec 10, 2023 at 9:42
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    $\begingroup$ @Woody There are many shutter constraint requirements for USOS windows to prevent contamination. Offgassing from visiting vehicles and recently flown payloads, thruster firings, and purges all require the Cupola windows and WORF to be shuttered. The Increment Lead OC is responsible for maintaining a spreadsheet with the amount of time WORF is open during various contamination "rate" scenarios - like how many visiting vehicles and where they're docked/berthed. If the area under the curve reaches a certain limit for a calendar year, the shutter must remain closed for the remainder of the year. $\endgroup$
    – Doresoom
    Feb 14 at 18:41

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