I have a copy of the Health & Safety Laboratory's (HSL) report of their inspection of the Redpoint descender involved in the incident at the Westway in Jan 2007, obtained from the Royal Borough of Kensington and Chelsea (RBKC) under the Freedom of Information Act.
I consider that the information and quotes that follow, fall under the fair use of copyrighted material.
The short version is that the no problem was found with the descender.
A service label on the descender indicated "last Factory Service 03-08-06". Entre-Prises website indicates the Redpoint requires annual servicing. The point here is that the descender would appear to have been serviced less than six months before the incident. Even if you assume the date is in American format (i.e. MM-DD-YY, which is unlikely as the same label had "date of manufacture 21-04-03"), the date would still be less an a year before the incident.
The descender was taken apart superficially by the HSL, who found nothing obviously untoward (although they noted the presence of "considerable amounts of particulate [...] in the brake assembly, it is assumed that this particulate was brake dust". The unit was then taken to Entre-Prises, where testing revealed it was functioning normally. It was then disassembled by people from Entre-Prises and MSA as far as they could (they lack the equipment/expertise to disassemble the hub assembly - they are supplied already assembled from the USA), who found nothing significantly wrong with the unit although "it was noted that the main unit gear was worn and it would have been expected to be replaced at next service" and "that the spring retention bar had been bent". There is nothing in the report to suggest that either of these factors could have caused a failure of the descender.
A key part, the one-way bearing (part of the hub assembly), was specifically "identified as the correct unit and not the potentially faulty one installed in some previous units". From the report: "It is possible that the one-way bearing may be the root cause of the incident, however, [sic] Entre-Prises have informed HSL that specialist equipment in the USA would be required to disassemble the descender further."
From the information I have, it appears that the investigation ended here - i.e. the descender was not sent to the USA to be further disassembled.
The only thing that raises a question in my mind (and note that my expertise in mechanics/engineering extends as far as "Hit it with a hammer until it works again!") is the brake dust, which led me to wonder if the brake pads would fail to engage the enclosure properly if there was too much brake dust in the assembly (the descender was tested AFTER it had been part-disassembled by the HSL, so one can assume that some of the brake dust would have fallen out - thus it would have been tested with less brake dust inside it than it had at the time of the incident). The recommended service interval on these things is a year - the amount/frequency of usage isn't mentioned in the same way that, for example, car manufacturer's recommend servicing once a year or every X,000 miles, or rope manufacturers recommend retiring a rope after it's taken X falls.
However -
1. This possibility (i.e. that the amount of brake dust caused the brake pads to fail to brake properly) is not mentioned in the report at all.
2. There is a hole at the bottom of the brake enclose to allow brake dust to escape. This hole was clear.
3. The quantity of brake dust inside the brake hub "was considered to be normal".
4. The RBKC's notes indicate that Entre-Prises "could not come up with a possible scenario where the descender would fail".
5. I am neither an engineer or a mechanic and, therefore, I don't have a scooby what I'm talking about.
So there you have it - it would appear that the root cause of the accident will remain a mystery.
