The flying Gas Bottle

M. Bieler, DESYWAO 2007

Trieste, Italy26.9.2007

Years ago in an Accelerator Lab in Hamburg…

• The Setup: Magnetic measurements on a new 1 Tesla superconducting

solenoid magnet.

• The Scenario: The cryo system ran out of helium. A quench was imminent. No

time to ramp down the magnet (~ 10 minutes).

• The Solution: A fresh gas bottle with 50 liter helium at 200 bar was needed.

Initial Problems• Problem #1: The gas bottle on a trolley had to pass by the magnet to get to the

cryo system. The magnet had a huge stray field.

• Solution #1: Carry the bottle low on the ground with the safety officer as a guard.

• Problem #2: The new bottle was marked as helium, but contained a different

gas.

• Solution #2: The safety officer himself brought in a new bottle.

The Accident

The safety officer, who was also the technical coordinator of this experiment, was in a hurry now to avoid the imminent quench of the magnet.

He stumbled, the bottle got nearer to the magnet than foreseen and was attracted by the magnet.

The flying bottle pressed the safety officer against a hard object. He received a laceration on the forehead and a black eye.

Just after the Accident

The magnet is being ramped down. Someone holds the bottle to prevent it from falling out of the magnet.The magnetic measurement instrument (red) is destroyed.

The whole Scene

Reasons for the Accident

• Main Reason: When the safety officer stumbled, he was under

pressure of time to avoid a quench of the magnet.

• Additional Reasons:1. The pressure reading of the helium supply was out of

order. This created the hectic rush to avoid the quench.2. The cryo system was located behind the magnet, so that

the gas bottles had to pass by the magnet.3. One gas bottle carried two different labels.

Lessons learned(for the test stand)

• Don‘t modify safety rules in a rush.

The safety rules did not allow to bring in heavy

magnetic material while the magnet was on.• Unambiguous labels for gas bottles.• Helium bottle placed at the entrance of the

test stand.• Additional fence within the test stand for the

region with magnetic fields above 300 Gauss.

Lessons learned(for machine operation)

Later the solenoid was installed in one of the HERA experiments.

Temporary access to this area is managed by the machine operators.

• 10 minutes delay between switching off the magnet and temporary access.

• Warning signs (“High magnetic field”) switched by a reed relay in the field of the magnet.

• Thorough search for magnetic material after work has been carried out near the magnet.

• Fire extinguishers and breathing apparatus in this area only with plastic bottles.