When planning to fill a large enclosed chamber with hydrogen, oxygen and propane, and allow members of the public to voluntarily ignite the contents, we find it’s best to consider ways to decrease the likelihood of blasting out four foot by eight foot sheets of shattered polycarbonate at hundreds of feet per second. If you plan on igniting flammable gases for amazement and amusement (read: art), you really have to consider safety third, and certainly no lower than that.

We’ve taken a number of measures to reduce the risk of life and limb, the most important of which is the hydrogen chamber itself. There’s a lot less chance of someone burning their hand, face, neck, neck, chest or faux fur costume if they are physically separated from the fire by a plastic barrier.

But again we come back to the question: How do we avoid blowing up the chamber? The key is to understand what the maximal flow rate in cubic feet per minute (cfm) is of our bubble blowing devices, and the flash point of hydrogen. Hydrogen becomes flammable in air at concentrations of just 4%. So we built an air blower and duct system that creates positive pressure inside the chamber at roughly 50-100 times our hydrogen usage. In our case, our bubble machines will consume 3-4cfm of hydrogen. Therefore we have installed a blower system that will push around 400cfm of air into the chamber. This reduces the maximum hydrogen concentration in the chamber to less than 2%. In addition, we’ve mounted many nichrome ignitors (see Ben’s last post) to ignite any small pockets of hydrogen, either contained by or not contained by bubbles, before they can collect into a dangerous situation.

How would we know if a dangerous situation occurs before the gigantic explosion? We mount a detector on the wall of our chamber, at a level where we would want to shut down the project if gas somehow pooled from the ceiling down to the detector mount point. If the detector goes off, the project is shut down until the chamber returns to safe levels.

This entry was posted on Monday, April 7th, 2008 at 1:59 pm and is filed under Models, Workshop.