ISS ammonia leak scare

Ammonia is typically used as a coolant in spaceflight systems.
On 14 January 2015, an ammonia leak was detected in the US section of the International Space Station (ISS). Like all spacecrafts, International Space Station requires a rejection system to radiate the heat generated by its electrical systems into space. This is achieved by transferring the heat to a liquid, which can then be easily piped away via the station’s radiators. Ammonia is typically used as a coolant in spaceflight systems, and due to its low freezing point it makes a very efficient coolant and prevents the extreme temperatures in space from freezing the coolant in the lines, thus causing blockages.

This external ammonia-cooling system is known as the ETCS (External Thermal Control System). Inside the station, cool water transports heat away from the internal electrical equipment via two low and moderate-temperature loops (the LTL and MTL). This is known as the ITCS (Internal Thermal Control System). Due to its toxicity, the ISS designers purposely store ammonia outside, ensuring no direct contact between both refrigerating systems. Since the water cannot be directly piped outside the station, as it would freeze in the coldness of space, the heat from the internal water loops must instead be transferred to the external ammonia loop, via a piece of hardware called an Interface Heat Exchanger (IFHX). While there is no direct connection between the internal water loop and external ammonia loop via the IFHX, a failure scenario does exist whereby a breach of an IFHX could cause ammonia from the external loop to enter the internal water loop, from where it could enter the ISS atmosphere.

However, after several verifications where conducted in the cabin atmosphere, data showed the ammonia scare was merely a computer anomaly and the crew was back to work a few hours later.  If nothing else, the incident served to exercise the crew’s well-practiced procedures.

Two months earlier, on 19 November 2014, R218, the refrigerant used in the station’s air-conditioning system was accidentally vented in the Russian section of the IIS, but the amount was negligible and the station filtration system will ‘scrub’ the refrigerant from the air supply.