Editing Submarine (section)

===Life support systems===
With [[nuclear reactor|nuclear power]] or [[air-independent propulsion]], submarines can remain submerged for months at a time. Conventional diesel submarines must periodically resurface or run on [[Submarine snorkel|snorkel]] to recharge their batteries. Most modern military submarines generate breathing [[oxygen]] by [[electrolysis]] of fresh water (using a device called an "[[Elektron (ISS)#Elektron|Electrolytic Oxygen Generator]]"). Emergency oxygen can be produced by burning [[sodium chlorate]] candles.<ref name="Smarter every day 251" >{{cite AV media|url=https://www.youtube.com/watch?v=g3Ud6mHdhlQ |title=How Do Nuclear Submarines Make Oxygen? |publisher= Smarter Every Day 251 |first= |last= |type=video |website=www.youtube.com |date=21 February 2021 |access-date=26 January 2022}}</ref> Atmosphere control equipment includes a [[Carbon dioxide scrubber]], which uses a spray of [[Amine gas treating|monoethanolamine]] (MEA) absorbent to remove the gas from the air, after which the MEA is heated in a boiler to release the CO<sub>2</sub> which is then pumped overboard. Emergency scrubbing can also be done with lithium hydroxide, which is consumable.<ref name="Smarter every day 251" /> A machine that uses a [[catalyst]] to convert [[carbon monoxide]] into carbon dioxide (removed by the {{CO2}} scrubber) and bonds [[hydrogen]] produced from the ship's storage battery with oxygen in the atmosphere to produce water, is also used.{{citation needed|date=January 2022}} An atmosphere monitoring system samples the air from different areas of the ship for [[nitrogen]], oxygen, hydrogen, [[Dichlorodifluoromethane|R-12]] and [[1,2-Dichlorotetrafluoroethane|R-114]] refrigerants, carbon dioxide, [[carbon monoxide]], and other gases.<ref name="Smarter every day 251" /> Poisonous gases are removed, and oxygen is replenished by use of an oxygen bank located in a main ballast tank.{{citation needed|date=January 2022}}{{clarify|Is storage of oxugen banks in main ballast tanks a common arrangement, or a special case?|date=January 2022}} Some heavier submarines have two oxygen bleed stations (forward and aft). The oxygen in the air is sometimes kept a few percent less than atmospheric concentration to reduce fire risk.

Fresh water is produced by either an evaporator or a [[reverse osmosis]] unit. The primary use for fresh water is to provide feedwater for the reactor and steam propulsion plants. It is also available for showers, sinks, cooking and cleaning once propulsion plant needs have been met. Seawater is used to flush toilets, and the resulting [[Blackwater (waste)|"blackwater"]] is stored in a sanitary tank until it is blown overboard using pressurized air or pumped overboard by using a special sanitary pump. The blackwater-discharge system requires skill to operate, and isolation valves must be closed before discharge.<ref name="Smarter every day 256" >{{cite AV media |url=https://www.youtube.com/watch?v=SYFuA3xnkUE |title=How to Poop on a Nuclear Submarine (256)|publisher=Smarter Every Day |type=video |website=www.youtube.com |date=9 May 2021 |access-date=27 January 2022 }}</ref> The German [[Type VII submarine|Type VIIC]] boat {{GS|U-1206||2}} was lost with casualties because of [[human error]] while using this system.<ref>{{cite web|url=http://www.uboat.net/boats/u1206.htm|title=U-1206|publisher=Uboat.net|access-date=18 April 2010}}</ref> Water from showers and sinks is stored separately in "[[greywater|grey water]]" tanks and discharged overboard using drain pumps.

Trash on modern large submarines is usually disposed of using a tube called a Trash Disposal Unit (TDU), where it is compacted into a galvanized steel can. At the bottom of the TDU is a large ball valve. An ice plug is set on top of the ball valve to protect it, the cans atop the ice plug. The top breech door is shut, and the TDU is flooded and equalized with sea pressure, the ball valve is opened and the cans fall out assisted by scrap iron weights in the cans. The TDU is also flushed with seawater to ensure it is completely empty and the ball valve is clear before closing the valve.{{citation needed|reason=Totally plausible, but a reference would be nice|date=January 2022}}