The Scott Air-Pak SCBA is an open-circuit,

self-contained breathing apparatus A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder. They are typically used in firefighting a ...

designed to meet the

National Fire Protection Association The National Fire Protection Association (NFPA) is a U.S.-based international nonprofit organization devoted to eliminating death, injury, property damage, and economic loss due to fire, electrical, and related hazards. , the NFPA claims to have 5 ...

(NFPA) Standard 1981. All components, excluding the air cylinder, were designed and manufactured by Scott Safety. Formerly a division of Tyco International, Ltd., Scott Safety was sold to 3M in 2017.

30 minute Cylinder specifications

Other sizes sold are 45, 60 & 75 minute cylinders. The cylinder and valve assembly is used for storing breathable air under pressure. *Dimensions: :a. Cylinder = 19.6” × 5” :b. Water capacity = 285 cubic inches :c. Air capacity = 45 cubic feet (1,280 L) for a 30-minute air supply (1274 liters) :d. Weight = 11 pounds (5.0 kg) :e. Weight with AP-50 = 23.7 pounds (10.8 kg)

Testing/burst hazards (Data for 4500 cylinders, 5500 cylinders also exist)

The burst pressure for the tri-dimensional burst disk used in the Scott is 4800

psi Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ or ψ), the twenty-third letter of the Greek alphabet * Psi (Cyrillic), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviat ...

. Carbon composite cylinders are made up of an aluminum alloy inner shell with carbon composite wraps and epoxy resin. They have a burst pressure of 12,000 psi, 6,500 without the carbon composite wrap.

Valve assembly

The valve assembly is the appliance which will make the connection between the cylinder and the hose (which will send the air to a pressure reducer). It is constructed of forged aluminum alloy, and is angled to reduce stress of the connection made between the high-pressure female coupling of the high pressure hose. Newer cylinders contain a "tri lobe, ergonomically designed hand wheel."http://www.southportland.org/vertical/Sites/%7B7A5A2430-7EB6-4AF7-AAA3-59DBDCFA30F2%7D/uploads/%7B1E27576C-6577-4B1A-B326-31B57B6EA2F8%7D.PDF This hand wheel is a one-way, ratcheting type knob which is a push to close style knob. This protects the user from unwanted accidental shutoff during use. There is also "an upstream connected frangible disc safety relief device" located on the valve assembly which is also known as the "tri-dimensional burst disk". This burst disk protects the user against a situation where the pressure in the bottle would increase with exposure to heat during a fire. It prevents unwanted failures somewhere else in the bottle. It is set to release at 7200 psi, or 400 ° F. It is "tri-dimensional" in that, if it is activated, it would disperse the air from the bottle in three directions so as not to throw the user off his or her balance.
The high pressure male coupling, included in high pressure bottle connections, is set to meet the

Compressed Gas Association The Compressed Gas Association (CGA) is an American trade association for the industrial and medical gas supply industries. The CGA publishes standards and practices that codify industry practices. In cases where government regulation is inspec ...

Standards #346 and #347.
Also included in the assembly are the dual-sided pressure gauge (which reads the cylinder pressure directly from the cylinder), elastomeric bumper (a protective, rubber like stop), and hangar plate (for positive locking attachment of the assembly to the backframe).

Effect of temperature on pressure gauge readings

The pressure gauge's indicated gas

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

changes with ambient

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

. As temperature decreases, the pressure inside the cylinder decreases. The relationship between the temperature and the pressure of a gas is determined by using the formula ''PV'' = ''nRT''. What is particularly important to understand from the formula is that the temperature is in

kelvin The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...

s, not degrees

Fahrenheit The Fahrenheit scale () is a scale of temperature, temperature scale based on one proposed in 1724 by the German-Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accou ...

. Consider the freezing point of water at 32 degrees Fahrenheit (0 degrees

Celsius The degree Celsius is the unit of temperature on the Celsius temperature scale "Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point ...

) and compare it to 96 °F (35.6 °C; normal human body temperature is 37 °C). While 96 is arithmetically three times 32, the difference in temperature from a scientific point of view is not threefold. Instead of comparing 32 to 96, temperatures of 273.15 K and 308.71 K should be compared.Online Conversion – Temperature Conversion
/ref> The actual scientifically valid change in temperature from 32 to 96 °F is by a factor of 1.13 (308.71/273.15), not 3. If an air cylinder is pressurized to 4,500 psi at 96 °F and later the temperature drops to 32 °F, the pressure gauge will indicate 4,000 psi (4,500/1.13). Stated differently, a drop in temperature of 10 degrees Fahrenheit causes a pressure decrease of about 82 psi.

References

{{DEFAULTSORT:Scott 2.2 3.5 4.5 Air-Pak SCBA Self-contained breathing apparatus Firefighter tools