There are three types of respirators or breathing air systems @ breathesafety that confined space rescuers tend to use namely, Self-Contained, Airline Supplied Respirator (SAR), and a combination of two known as Type C. Each of these respirators has its own set of pros and cons when in use at the time of rescue.
Self-Contained Breathing Apparatus (SCBA, open circuit)
An SCBA features a cylinder holding breathing air under pressure and placed on the back of the wearer through a harness. This is something that all types of SCBAs tend to have in common although they all are available from different manufacturers and contain various features to render themselves unique from their competitors.
In the cylinder, the air kept under positive pressure passes from it via a pressure-reducing regulator and reaches to a face piece for breathing. The wearer of the apparatus breathes the air and exhales the used air into the atmosphere, due to which it is known as an open circuit SCBA. The OSHA or Occupational Safety and Health Administration has termed such a breathing apparatus as fire style breathing apparatus.
To be an SCBA, the cylinder needs to have a minimum capacity of half an hour, which is determined from its flow rate of 40 liters of air per 60 seconds. The typical pressures are 2,216, 3,000, and 4,500 Pounds per Square Inch (PSIG) on gauge. The rated capacities can differ from half an hour to one hour.
Pros: Highly portable to go anywhere with the wearer, readily available within most business and industry facilities
Cons: Supply for limited duration, reduced cylinder capacity due to wearer’s exertion and physical conditioning, more weight with 25 pounds even with high-pressure and low profile units, risk of dropping cylinder
There are also closed-circuit SCBAs that work by generating oxygen via a chemical reaction triggering between the oxygen generating chemical and moisture in exhaled breath. The generated oxygen is kept in a breathing bag before inhaling. Such units are known as Oxygen Breathing Apparatus (OBA) wherein all air exhaled is recirculated in the unit due to which they are called closed circuit SCBAs. Alternatively, these units work by using a small cylinder of compressed oxygen for improving exhaled air.
Pros: Portability and higher usage time
Airline-Supplied Respirator (SAR)
An SAR for confined spaces usually has its own wearing harness and an emergency escape bottle ranging from a 5- to 20-minute capacity. It needs to be supplied from a stored, compressed source of air directly. Such units have two air sources for the rescuer, escape bottle and airline supply, rather than a single source by SCBA. In case the primary source of supply fails, the escape bottle becomes handy for the rescuer.
Pros: Different air sources, portable, compact due to a lower profile than SCBA
Cons: Limited travel distance up to 300 feet of hose, entanglement of hose with machinery
Type C Airline/SCBA
This one is a fire department-style, self-contained apparatus with a minimum capacity of 30 minutes. It features a connection that allows affixing an airline to an external source of air.
Pros: Portable, two sources of air namely, 30-minute air bottle and airline supply
Cons: Too bulky, hose entanglement in confined spaces, risk of dropped cylinder