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These tests were conducted in part for the ME406 technical elective course at Portland State University on high altitude balloon experiment design. This year's experiment team pursued a panoramic imaging system (see LPSU 08 mission) that also included a first Hydrogen balloon fill and launch from an urban site  (i.e. downtown Portland Oregon). A significant effort was made to investigate potential hazards of this approach before these tests. The full safety analysis and plan (by Matt) is attached below. The advantages of using hydrogen have  been suggested elsewhere which include its lower cost, but mostly to reduce the worldwide depletion rate of Helium which might be used for more essential rather than merely educational purposes.

These are notes taken from LPSU-er and Oregon Mountaineer, Physicist, Astonomer, Electrician, etc....Robert McGown...

H₂ Balloon Deflagration Test, Smith Berry Barn, Scholls, Oregon, May 21, 2007

The PSU ballooning team assembled for H₂ deflagration balloon tests in a rural Oregon setting. Their goal was to educate and access the safety margins of hydrogen ballooning for high altitude autonomous experiments. We set up a launch pad and ground plain to allow the equalizing of any spark potential or static discharge, on an open grassy pasture. Three ground rods were driven and the grounding of the tank, ground matt, and rods were equal. #8 solid cu was used for the ground plane and #4 cu stranded was used for the three ground rods.

Latex balloons were filled and ignited with a magnesium flare by lowering the balloon down by pulling on the tether string. Two concrete piers were used as a pulley to drag the balloon on to a flare. There was about a 10 mph intermittent breeze that pushed the balloons over on a about a 15 degree deflection after they were filled and readied for ignition.    

Managing the balloons was a difficult task with two balloons waiting to be ignited, tethered about 35 feet and 45 feet above the ground on an uneven tether so the balloons wouldn’t tangle or collide (see pics).

Balloon One was filled to a diameter of 5 feet with at a temperature of 30 degrees from the bottle. The air temperature was about 70 degrees. The Sun, low on the horizon, came out periodically bathing the balloons with protons and electrons. This was just a verbal check. The balloon was lowered down on to the lit magnesium flare and it ignited with three attempts on the side of the balloon. A large fireball ignited upward and the entire balloon peeled the onion skin away in burning flame. The balloon came down in one piece on fire, burning the rubber latex and a 2 ft hole through the launch pad. A great gaseous ball of fire floated at an angle upward 18 feet and dissipated rapidly!

Balloon Two was filled up to a diameter of 7 feet and the neck stretched out by five feet. The same process was used to lower the balloon by pulling the string down. This time there was more lift pulling a 25 lb block off the ground, so we used a second block. This ignition test on the magnesium flare caused a fire ball that rose to 40 feet. The real danger was the falling pieces of burning latex rubber that fell like burning leaves from the sky. They landed in a 20 ft diameter radius off set from the balloon. The balloon team immediately put out the burning latex on the ground.

Matt Baker built a test dummy that was a likeness of a local bully that was used at the ignition site. There was not much of a shock wave at all. The heat did not affect the test dummy at ground zero. Two card board boxes appeared to be knocked over on the first test and not the second test. There was some free H2 in the air in the filling and hose purging process.

After the test, three team members pulled the ground rods out of the soil and the team disassembled the launch pad. It was a successful and safe test.

Balloon stats...
Balloon #1     117 cubic feet    7.35 feet diameter
Balloon #2    164 cubic feet     8.23 feet diameter