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While the model developed in this paper describes cylinders which have a rapid mode of crack
growth, the model apparently does not apply to the vast majority of cylinders which do not fail in
traffic. There must be additional effects which have not yet been identified which will make some
cylinders follow a faster mode of crack growth.
The paper also shows that the classical fracture mechanics approach suggests that there will be
"leak before break" for the cylinders. However, there have been cases were there have been no
precursor leaks before a violent failure. The paper shows that the growth of the defects is not
necessarily uniform along the crack front and this leads to the possibility of burst before leak.

REFERENCES

1. Ibrahim, R. N., Ph.D. Thesis, University of New South Wales, School of Mechanical and Industrial Engineering, 1990.
2. Lewandowski, J. J., Kim, Y. S. and Holroyd, N. J. H., Metallurgical Transactions A, 1992,23A, 1679-1689.
3. Lynch, S. P., Materials Science and Engineering, 1989, AlOS, 203-210.
4. Failure Analysis Associates, Examination of Scott Air-Pak cylinders. Los Angeles, 31 May 1984.
5. NIOSH, U.S. Department of Health and Human Services (DHHS), Respirator Users Warning, National Institute for
Occupational Safety and Health (NIOSH), Division of Safety Research, Morgantown, WV, 21 July 1983. See also
Safety advisories: Federal Register, Research and Special Programs Administration Notice 93-22, Vol. 58, No. 221, 18
November 1993, and Notice 94-7, Vol. 59, No. 142,26 July 1994.
6. Diuer News, United States commercial publication, September 1994.
7. Poole, R., Professional Diver Journal, 1995,1( 1). Sydney, Australia, Winter.
8. Stark, H. L. and Ibrahim, R. N., Engineering Fracture Mechanics, 1992,48,569-574.
9. Price, J. W. H., Ibrahim, R. N. and Ischenko, D., Int. ConJ on Pipes and Vessels, Singapore, February 1996.
10. Stark, H. L. and Ibrahim, R. N., Engineering Fructure Mechanics, 1988,30(3), 409.
11. Price, J. W. H., Ibrahim, R. N. and Ischenko, D., Pressure Vessel Technology Conference. ASME, Montreal, July 1996.
12. Schr6der, R., Materials Science and Technology, 1985, l(Oct), 154.