Connecting theme, science concepts and the curriculum
In any mixture of gases the total pressure is simply the sum of the pressure of each of its individual components. For example, in air at standard pressure and
temperature (STP, 101.3kPa and 0oC) and 50% relative humidity, air is composed of the gases as shown above.
In principle, a human could live easily in an atmosphere with a total pressure of
21kPa provided that it was composed of pure oxygen! The reason that we could live with an atmospheric pressure of only 21kPa (pure oxygen) is because at sea level the Earth’s atmosphere only contains about 21kPa of oxygen (In other words, at sea level, the partial pressure of oxygen is 21kPa). Breathing oxygen at a partial pressure of 21 kPa is the same from a biological point of view with or without nitrogen.
The earliest manned spacecraft and present day EVA space suits make use of this fact.
There are two main reason for this:
- It is easier to design structures which can withstand an internal pressure1 of
21kPa than it is to design structures which can withstand an internal pressure of 101kPa.
- By leaving the nitrogen component out of the breathing air, the weight of the gases needed to be launched into orbit is reduced by about 80%.
Unfortunately, a pure oxygen atmosphere, even at reduced pressure, causes rapid and uncontrolled combustion if a fire should occur. Combustion is so intense that even metals burn once ignited. Without the “quenching” effect of nitrogen a pure oxygen atmosphere
poses a serious fire hazard. For this reason astronauts in both the Space Shuttle and the International Space Station are provided with a nitrogen rich environment.
Curriculum Expectation: Analyse and describe examples where technologies were developed based on scientific understanding.