Today I plan on doing 425 feet (130 meters). My previous deepest is 407 feet .
AND a little FYI:
Where does helium come from?
(Lansing State Journal, April 27, 1995)
There is helium all around us in the air, but it is not a good source for helium collectors. There are only about 5 parts of helium for every 100,000 parts of air! People have discovered much richer sources of helium underground. Some radioactive elements, such as uranium, release alpha particles when they decay. An alpha particle is just a helium atom with no electrons. Deep in the Earth where these radioactive decays take place, the alpha particles capture electrons and become helium. As the radioactive deposits age, large quantities of helium become trapped in underground caverns. To collect the helium, people drill down into the caverns and capture the helium as it escapes.
Most people are familiar with helium balloons. We put helium in these balloons, because it is lighter than air and is non-flammable. However, most of the helium used today is in liquid form. All gases become liquids when the temperature becomes low enough, or when excessive pressure is used. Scientists use liquid helium for experiments that have to be kept very very cold. Helium becomes a liquid at 270oC below zero!