NESC tech bulletin

National Aeronautics and Space Administration

www.nasa.gov

NASA Engineering and Safety Center Technical Bulletin No. 09-05

NESC-TB-09-05

Applicability

This information is applicable to military and aerospace 

SCOGs.

Background

SCOG failures were recently investigated by the NASA 

Engineering and Safety Center (NESC) as a result of an SCOG 

explosion aboard the United Kingdom’s Royal Navy submarine 

HMS Tireless. The root cause identified during this investigation 

was contamination of the internal briquette. When the briquette 

is contaminated, it can result in a runaway pressure event, 

which can lead to an SCOG explosion. 

Findings and Conclusions

Liquid organic (oil) contamination can cause excessive heating 

and an increased burn rate in SCOGs. Contamination also 

contributes to an accelerated pressure increase, which does 

not allow the containment system to vent the accelerated 

pressure increase effectively. 

A history of overheating and faster burn rate areas attributed to 

uneven mixing of the chemicals in the briquette was identified 

in SCOGs. The chemical mixture in the briquette contains iron 

filings that act as an accelerant for the SCOG reaction. When 

the iron is not uniformly distributed in the briquette mixture, 

the result will be locally enriched “hot spots” with faster burn 

rates. 

An additional area of concern with the design of the SCOG 

containment system was identified. Systems that have an 

undersized venting mechanism could fail as a result of pressure 

runaway. This pressure runaway is caused when the gas is 

generated in the SCOG faster than it can be vented from the 

containment system. 

Corrective actions were identified for the safe operation 

of SCOGs, one of which was to prevent organic material/

fuel contamination. Contamination should be prevented by 

maintaining the briquette seals and storing away from organic 

materials. The briquette should be tested for uneven mixing 

of iron additives. Another corrective action was to design the 

containment system in a manner that allows the pressure to 

escape during the chemical reaction. There are a variety of 

possibilities for the containment system for a SCOG. The United 

States Navy uses an open containment system for their SCOGs 

and this system has been working successfully.

Reference

Self-Contained Oxygen Generator Safety Assessment: Effects 

of Organics Contamination, Briquette Fracturing, Pressure 

Containment and Variations in Chemical Composition. NESC 

Assessment Number: 07-051-E, October 2008

WSTF-IR-1120-001-08 Self-contained Oxygen Generator 

Investigation, Analysis and Testing

This work was led by Henry Rotter and John Graf, Johnson Space 

Flight Center, and by Jon Haas, White Sands Test Facility.

For information contact the NESC at www.nesc.nasa.gov

Space Station Backup Oxygen Candle System (4” x 4” square candle)

(Far left) Test cell candle 

initiation in 8’ x 8’ test cell with 

Lexan flexible sheets

(Left) Duplication of explosion 

on the Royal Navy submarine 

(Note: destroyed Lexan sheets)

Self-Contained Oxygen Generator: Effects of Organic

Contamination, Briquette Fracturing, Pressure Containment,

and Variations in Chemical Composition

A Self-Contained Oxygen Generator (SCOG) produces breathable oxygen (O

2

) by using chemically-reactive briquettes 

that begin producing O

2

 when mechanically ignited. Contamination with organic material of, or manufacturing 

defects in, the briquettes have been shown to lead to conditions that can cause an explosive failure