In human spaceflight, a life support system is a group of devices that allow a human being to survive in space. US government space agency NASA, and private spaceflight companies use the term environmental control and life support system or the acronym ECLSS when describing these systems for their human spaceflight missions. The life support system may supply air, water and food. It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical, and are designed and constructed using safety engineering techniques.