Report on damage MDT chambers in a Crane Accident
on Nov. 24. 2004
The University of Michigan Atlas Group
Curtis Weaverdyck from University of Michigan was witness to the following accident in
the afternoon (around 2pm) on Nov. 24, 2204. He just walked in Building 180 and saw
that the CERN riggers were moving two Michigan EML4 MDT chambers (EML4A07
and EML4C07) from the truck into storage with one chamber box stacked on the other.
The chamber-load started to swing slightly during horizontal transport with the load at a
height of about 8 meters. The top box slipped on the bottom one, over balanced and fell.
It ended up at about a 45 degree compound angle with one end on top of a coil casing
(about 3m above the floor) and the other end wedged against a set of concrete blocks.
The read-out end of the chamber had punched out the end plywood and was extending
about 30cm out of the box. The outermost tube on the long side was dented in, flattened,
over a 20cm length, by about a half radius. Fig. 1 shows the chamber box where it came
to rest. About 4 meters from this end of the box, on the same side, is a 10cm hole in the
side of the box where it was impaled on a pipe during the fall (see Fig. 2). The pipe
impaled several tubes in the bottom Multi-Layer of the
chamber.
Figure 1. EML4A07 dropped on concrete blocks.
Figure 2. A pipe penetrated into the box when
chamber was dropped, making this hole.
Incidentally, the second box, on the bottom of the crane, did not fall, but ended up
hanging from the slings where they caught on the feet of the box, with the tubes in a
vertical orientation.
Curtis called Michigan crew to Building 180 and Alan brought his camera to record. We
tried to communicate our concern for avoiding further damage to the chamber to the
riggers as they re-lifted the box. They did not take our suggestions, but they did not do
further damage as they lifted the box.
The cause of the accident was clearly unsafe rigging. They used a narrow spreader-frame
(pallonier) with the same width as the chamber boxes so that the slings apply almost no
friction on the upper box.
Figure 3. The spreader-bar was incorrectly used.
Figure 4. Crashed tubes on EML4A07 long tube
section
Assessment of the chamber damage after opening the dropped boxes
Damage on EML4 A07
1)
As shown in Fig. 4, three of the longest tubes in ML2 were crashed.
(Tube IDs: tube-layer 1, tube numbers 63 and 64, and tube layer 2, tube number
64). These three tubes are not repairable.
2) On the same side, the ML1, layer 2, tube 64 is dented at its midpoint.
3) On ML2, tube-layer 1, about 16 tubes were badly dented, near the short edge.
4) Chamber spacer-frame structure is broken as shown in Fig. 5.
The spacer-frame thin-edge is crashed at the HV end, near the short side. The glue
to hold the ML2 on the spacer frame is broken by about 60 cm along the glue strip.
The damage totally destroyed chamber wire precision. It is not
clear if we could repair the chamber with enough mechanical strength.
5)
On short side of the bottom tube section, 10 tubelets of the gas system were
crushed, resulting in huge gas leak on chamber.
6)
The chamber crating box has been badly damaged (deformed). It
can not be used to box the chamber for transportation and storage.
Repair of the gas system and the chamber structure is estimated to take at least two
months. Further tests and X-ray tomography to determine chamber precision will take
another month. Some damages are not repairable. The precision placement of the wires
is impossible to regain.
Figure 5.
Broken joint between ML2 and
Spacer-
frame on
EML4A07. 16 tubes which were dented
can be observed too.
Figure 6.
Damaged
Faraday Cage hides the
crushed thin web of the spacer frame. Inside
the FC are crushed gas tubelets.
Figure 7. Damaged tubelets on EML4A07 ML2
shortest section resulting in huge leak.
Figure 8.
EML4A07
crating box has been
damaged.
Damage on EML4 C07
This chamber was hanging vertically from the crane after the top chamber (EML4 A07)
had fallen. The damage which is visible at this time on this chamber is on the bottom gas
system, which is crushed at the readout end, resulting in huge gas leak. Detailed damage
cannot be seen clearly until the chamber is mounted in a rotating frame and the bottom
surface is accessible. We have to re-build the chamber rotator cart for further assessment
check. Repair and testing of the chamber gas system is estimated to take about two
months of time for two persons. If damage to the tubes is found, the Multilayer may be
damaged beyond repair.
Cost estimate
Total cost to rebuild a new EML4 chamber would require at least $100,000. (to pay for
the tooling, materials, services, and manpower).
Examination of the damage to these two chambers is still preliminary, limited to simple
tests and visible portions of the chambers. Damage estimates are subject to revision
when further tests can be performed.
Damage cost of EML4 A07 is estimated at $50,000, and repairing of EML4 C07 is
estimated to cost $20,000 if further damage is not found. As stated earlier, some part of
the chamber will not be repairable.
