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 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. Breathing set appears to be a secondary synonym for breathing apparatus, as internet searches appear to all be redirected to breathing apparatus. According to Merriam-Webster, a ventilator can be a medical device to provide artificially assisted respiration, or equipment to circulate fresh air through a space, while a respirator is usually a mask worn to protect the user from particulate contaminants in the air, but can also mean a device for providing artificial respiration. The usage in the sense of a filtering mask dates to the early 19th century and the artificial respiration sense dates to the second half of the 19th century, so both are well established. The UK Health and Safety Executive (HSE) distinguishes between respirators and breathing apparatus. Respirators are described as filtering devices, which may be powered, using a motor to pass ambient air through the filter, or unpowered, relying on the wearer's breathing to draw ambient air through the filter. The distinguishing features of a respirator in this context appear to be that the air is not significantly compressed at any stage, is filtered, and is at approximately ambient pressure. The HSE definition for breathing apparatus is that they use a supply of breathing quality gas from an independent source, such as air compressors or compressed gas cylinders. In this case compression of the supply gas at some stage is implied. Both respirators and breathing apparatus are classed as respiratory protective equipment by the HSE. Vocabulary.com describes a breathing apparatus as "a device that facilitates breathing in cases of respiratory failure", which is a functional description of a medical ventilator, or a resuscitator. McGraw-Hill Dictionary of Scientific & Technical Terms defines breathing apparatus as "An appliance that enables a person to function in irrespirable or poisonous gases or fluids; contains a supply of oxygen and a regenerator which removes the carbon dioxide exhaled", which is the description of any type or application of rebreather.
Breathing gas source The US Occupational Safety and Health Administration (OSHA) uses the source of the breathing gas to distinguish between types of breathing apparatus, and considers respirators to be a type or class of breathing apparatus: An atmosphere-supplying respirator is a breathing apparatus that supplies the user with breathing gas from a source independent of the ambient atmosphere, such as supplied-air respirators (SARs) and self-contained breathing apparatus (SCBA). A self-contained breathing apparatus (SCBA) is a type of atmosphere-supplying breathing apparatus in which the breathing gas source is carried by the user. A supplied-air respirator (SAR), or airline respirator, is a type of atmosphere-supplying breathing apparatus which uses a hose to supply breathing gas from a source which is not carried by the user. An air-purifying respirator is a breathing apparatus which uses a filter, cartridge, or canister, to remove specific air contaminants by passing ambient air through the air-purifying component. No distinction is made based on the mechanism of passing the air through the purifying component – it may be the lungs of the user or a mechanical device. The breathing gas source may be the ambient atmosphere, compressed air supplied from a low pressure compressor in real time, oxygen enriched air supplied from an oxygen concentrator, high-pressure stored compressed air, supercritical compressed air, oxygen or blended gas mixtures, liquid oxygen, chemically generated oxygen, or a combination of ambient atmosphere and another of these sources.
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