Milestones in Mining Safety and Health Technology

NIOSH MINING SAFETY AND HEALTH RESEARCH 

Technology

No. 55

News

5 December 2016

New Very High-Pressure Oxygen Cylinders for Use in 

Closed-Circuit Self-Contained Self-Rescuers (SCSRs)

Summary

New materials have allowed for a 

reduced size and weight of compressed 

gas cylinders that store pure oxygen at 

high pressures, giving manufacturers 

of closed-circuit self-contained selfrescuers (SCSRs) improved options for 

meeting the new standard for oxygen 

consumption requirements set forth in 

42 CFR Part 84 Subpart O. These newly 

designed very high-pressure cylinders

—currently Department of Transportation (DOT)-certified for oxygen duty 

to 3,000 psi and now available in two 

sizes—will enable manufacturers to 

reduce the overall size and weight of 

future SCSR units by incorporating 

these cylinders in their designs. Using 

this new cylinder technology at 3,000 

psi represents a significant advancement, affording greater SCSR design 

flexibility by allowing manufacturers 

to choose between cylinders with 

two length dimensions, using them 

singularly or in combination, which 

will enable different capacities and 

therefore different operational durations for SCSR designs. Moreover, the 

new cylinder technology was designed 

to be capable of meeting DOT certification for 5,000 psi oxygen duty. Therefore, SCSR manufacturers can pursue 

DOT certification for use at 5,000 psi to 

further reduce the size and weight of 

their devices beyond what is already 

achievable at 3,000 psi.

By Rohan Fernando

Need for Improved Breathing Air 

Supply (BAS) Technologies

The Mine Improvement and New Emergency Response Act of 2006 demonstrated a need to move SCSR technology to 

a next-generation status. In response to 

this need, NIOSH established a Breathing 

Air Supplies (BAS) program to develop 

components that could be used in nextgeneration SCSR devices by:

►allowing users to change between 

breathing apparatus using docking/

switch-over valves without exposure 

to a non-respirable atmosphere

►enabling verbal communications 

through the use of hoods and/or 

masks

►addressing performance efficiency 

improvements in SCSRs by focusing 

on specific design areas

►providing more ergonomic SCSR designs to improve the user experience

►exploring alternative solutions to 

SCSR caches along the escape route

Very High-Pressure Oxygen Cylinders

SCSRs used in mines for self-escape

post-disaster store and generate oxygen 

in one of two ways, leading to two design

types: chemical oxygen-generating 

types using potassium superoxide (KO2) 

and types using gaseous oxygen stored 

in a compressed form in high-pressure

cylinders. Current high-pressure oxygen 

cylinders used in NIOSH/MSHA-approved 

“one-hour” SCSRs store oxygen at 3,000 

psi (206 bar) and are manufactured out

of aluminum or composite materials.

Stainless steel cylinders used in NIOSH/

MSHA-approved “10-minute” SCSRs 

store oxygen at 3,850 psi (265 bar). 

With advances in materials science, two 

important opportunities exist: (1) to 

notably reduce the size and weight of 

cylinders filled to 3,000 psi, and (2) to 

significantly improve cylinder capacity 

by increasing cylinder fill pressure.

Figure 1: Two new manufactured cylinders 

that meet DOT requirements for use in SCSRs.

New Cylinder Designs

Two sizes of carbon composite cylinders 

with aluminum liners were manufactured 

(see Figure 1) to meet all relevant U.S. 

Department of Transportation (DOT) 

regulations. The capacity (or useable 

oxygen volume) to be contained in the 

cylinders was determined by considering 

two relevant standards:

►the oxygen consumption stated in the 

capacity and performance tables in 

42 CFR Part 84 Subpart O—i.e., three 

capacity ratings defined in relation to 

volume of oxygen (in liters) available 

in the device as Cap 1 (20 ≤ L ≤ 59), 

Cap 2 (60 ≤ L ≤ 79), and Cap 3 (L ≥ 80);
►the one-hour duration required by 30 CFR Part 75 for 

self-rescue devices used in mine escape applications.

To allow smaller cylinders to be used in an SCSR with a nominal 

duration of one hour or one-half hour while meeting the 

oxygen consumption requirements in 42 CFR Part 84 Subpart 

O, the design criterion for maximum service pressure was set at 

5,000 psi (345 bar). Two cylinder sizes were selected to contain oxygen with expanded volumes (at 1 atmosphere) of 140 

liters and 98 liters, respectively, at this pressure. Table 1 lists 

the oxygen capacities at different pressures for the two newly 

manufactured cylinders—the Luxfer L3B and Luxfer L3C.

Table 1. Cylinder oxygen capacities at different pressures

Cylinder

Nominal 

water volume 

(cubic inches)

Length 

(inches)

Diameter 

(inches)

Oxygen volume (liters) 

at service pressure (psi)

Luxfer L3B 19.7 6.5 2.7 98 L at 5,000 psi

70 L at 3,000 psi

Luxfer L3C 28.1 8.5 2.7 140 L at 5,000 psi

101 L at 3,000psi

For fill capacities of both 3,000 and 5,000 psi, the cylinders also 

provide a significant reduction in size and weight from that 

which is currently available on the market. The new cylinders 

described in this document represent a significant opportunity 

for SCSR manufacturers to address the size and weight concern 

in new SCSR designs. As an example, when considering only 

the 3,000 psi fill capacity, one could now develop a smaller 

and lighter Cap 3 device by using the L3C cylinder filled only 

to 3,000 psi. Moreover, as manufacturers design their SCSRs to 

meet the new standard, the need for a different layout/shape 

or longer-duration (140 L) Cap 3 SCSR may be desirable. In 

this instance, a manufacturer has the option of using two L3B 

cylinders in combination, each filled at 3,000 psi. In addition to 

the size and weight improvements discussed above when the 

cylinders are filled to only 3,000 psi, additional improvements 

will also be achievable if a manufacturer pursues DOT certification for filling to 5,000 psi. For this same example cited above, 

the L3C cylinder can be replaced with the L3B cylinder when 

pressurized to 5,000 psi, thus making the SCSR still smaller due 

to the reduced cylinder size for the same duration. The 5,000 

psi (345 bar) service pressure rating allows the required quantity of oxygen to be stored in a cylinder that could be used 

in a person-wearable one-hour SCSR despite the degrading 

effects of the compressibility factor of oxygen at that pressure. 

This pressure is within the capability of current oxygen-filling 

equipment, such as booster pumps.

New Cylinder Specifications

The new cylinders are fully wrapped filament-wound composite pressure vessels designed for a maximum service pressure 

of 5,000 psi (345 bar) and an operating service life of 15 years. 

They are constructed of a carbon fiber/epoxy resin composite 

overwrap of a 6061-T6 aluminum alloy liner. The outermost 

wrap of the cylinders consists of an S2-glass fiber/epoxy resin 

composite for abrasion protection. 

The cylinders have one port with an internal neck thread 

with an O-ring seal to accept a shut-off valve and/or pressure 

regulator. Both cylinders were manufactured to the following 

specifications: maximum service pressure of 3,000 psi (206 bar) 

for containing oxygen; maximum service pressure of 5,000 

psi (345 bar) for containing air, argon, carbon dioxide, helium, 

hydrogen, methane, nitrogen, and nitrous oxide; test pressure 

of 8,333 psi (575 bar); approval by DOT SP-10915; qualification 

tests according to DOT-CFFC; thread form of 0.625-18 UNF-2B. 

The following additional specifications apply to the Luxfer L3B 

cylinder: nominal diameter of 2.7 in (68.6 mm); nominal length 

of 6.5 in (164 mm); water volume of 19.7 cu. in (0.32 liters); 

maximum weight (empty) of 1.1 lb (0.50 kg). 

The following additional specifications apply to the Luxfer L3C 

cylinder: nominal diameter of 2.7 in (68.6 mm); nominal length 

of 8.5 in (216 mm); water volume of 28.1 cu. in (0.46 liters); maximum weight (empty) of 1.3 lb (0.58 kg). 

The material used in cylinder manufacture is oxygen compatible; however, cylinders must be internally cleaned for oxygen 

service according to MIL1330 or an equivalent standard before 

being integrated into a breathing apparatus.

Certification Testing

As part of the qualification process, the cylinders underwent a 

series of tests according to DOT-CFFC procedures. These were 

the hydrostatic test, hydraulic burst test, drop test, cycling test 

at ambient temperature, environmental cycle test, thermal 

cycle test, gunfire test, and bonfire test. The cylinders were tested at a DOT testing facility. Design approval certificates were 

issued for both cylinder types per DOT-SP10915, allowing the 

cylinders to be filled with compressed gas to 3,000 psi (206 bar).

Limitations/Restrictions

The current DOT approval for these newly developed cylinders 

allows a maximum service pressure of 3,000 psi (206 bar) for 

containing pure oxygen, which is the gas used in closed-circuit SCSR designs. The 5,000 psi (345 bar) pressure rating is for 

containing air and other gases. DOT approval for the 5,000 psi 

(345 bar) oxygen rating is being pursued by NIOSH, but until 

such approval is granted, these cylinders should be limited to a 

service pressure of 3,000 psi (206 bar).

Breathing Air Supplies Program Statement

As NIOSH continues to implement its Breathing Air Supplies 

program, we will continue to work with any interested manufacturers to help them produce compliant products to meet 

NIOSH and DOT standards.

Disclaimer

Mention of any company, product, or service is for informational purposes only and does not constitute endorsement by the 

National Institute for Occupational Safety and Health (NIOSH), 

the Centers for Disease Control and Prevention (CDC), or the 

U.S. Department of Health and Human Services (HHS), or imply 

that any company or its products or services are preferred over 

any other.

For More Information

To receive NIOSH documents or for more information about occupational safety and health topics, contact: 

1-800-CDC-INFO (1-800-232-4636), 1-888-232-6348 (TTY), or request information at the CDC website at 

www.cdc.gov/info, or visit the NIOSH website at www.cdc.gov/niosh.

DHHS (NIOSH) Publication No. 2017–111

For more information on this topic, contact Rohan Fernando (RFernando@cdc.gov, 412-386-6619) or the NIOSH Mining Program (mining@cdc.gov).