thumb|In an atmosphere that may be oxygen-deficient, or toxic, an air supply can be carried on the back.
thumb|Royal Navy commando in 1945
A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.
Breathing apparatus may be classified by type in several ways:
- By breathing gas source: self-contained gas supply, remotely supplied gas, or purified ambient air
- By environment: underwater/hyperbaric, terrestrial/normobaric, or high altitude/hypobaric
- By breathing circuit type: open, semi-closed, or closed circuit
- By gas supply type: constant flow, supply on demand, or supplemental
- By ventilatory driving force: the breathing effort of the user, or mechanical work from an external source
- By operational pressure regime: at ambient pressure or in isolation from ambient pressure<!--is there a standard term for this?-->
- By gas mixture: air, oxygen enriched air, pure oxygen or mixed gases
- By purpose: underwater diving, mountaineering, aeronautical, industrial, emergency and escape, and medical
The user respiratory interface is the delivery system by which the breathing apparatus guides the breathing gas flow to and from the user. Some form of facepiece, hood or helmet is usual, but for some medical interventions an invasive method may be necessary.
Any given unit is a member of several types. The well-known recreational scuba set is a self-contained, open circuit, demand supplied, high pressure stored air, ambient pressure, underwater diving type, delivered through a bite-grip secured mouthpiece.
Definition and scope
Semantically, the term breathing apparatus implies any set of equipment and materials specifically intended to enable or facilitate breathing, which could include equipment as basic as a snorkel or artificial airway, or as complex as an anaesthetic machine or a space suit. Actual usage varies, and breathing apparatus, breathing set, ventilator and respirator have similar and overlapping meanings which vary depending on the sources chosen.
Human factors in breathing apparatus design
Human factors in breathing apparatus design are the influence of the interaction between the user and the equipment on the design of the equipment. The user of breathing apparatus relies on the equipment to stay alive or healthy, in reasonable comfort and to perform the tasks required during use of the equipment. The design of the equipment can strongly influence its effectiveness in performing the desired functions. It should be comfortable to wear, and not cause stress injury or allergic reactions to component materials. It must be reliable and should not require constant attention or adjustment during use, and if possible performance should degrade gradually in the event of malfunctions, allowing time for corrective action to be taken with minimum risk.