Upon visual inspection of the failed filter canister, evidence of fatigue failure was found. A chemical analysis of the base material used to manufacture the failed filter canister showed it to be out of specification from the manufacturer's claims. The element that was slightly deficient in the analysis, copper, is known to strengthen the cited aluminum alloy (ASTM 024). A fatigue of the filter design was performed using dimensions measured from an exemplar filter canister that was sectioned and polished for this study, assumed applied loads, and the properties of on-specification ASTM 2024 aluminum. This analysis showed that the anticipated fatigue life of the subject filter housing was very sensitive to the composition of the material and to the machined radius of the lower-outer corner of the O-ring groove. The estimated fatigue life of this part was determined to be adequate (i.e. greater than 10⁷ cycles) if sufficiently long radii were consistently machined into the O-ring groove corners. However, the part life was estimated at less than three years if the shortest observed radii were consistently machined into the O-ring groove corners. Effects of gravity (as evidenced by the mounting arrangement and orientation of the filter housing) were determined to be negligible relative to the pressure loading. Neither the subject, nor the exemplar filter housings showed any evidence of 'bottoming out' or interference between the male and female portions, and as such, 'over-torquing' was ruled out as being a significant contributor to the observed failure. In order to identify other CNG filling components that may be at risk of failure, a Hazards and Operability (HAZOP) Review of the entire process (from the tie point to the local gas utility all the way to the filling nozzle that is connected to the vehicles being filled) was performed. Thirty-five specific deviations or hazards were identified and risk-ranked. Of these, none received a ranking of 'unacceptable' or 'undesirable', twelve received the ranking 'acceptable with controls' and the rest were ranked either 'acceptable as is', or 'not a problem'.