Burning Man Safety: How to Build a Flame Sensor
There is a secret truth that we all suspected as children, but which our parents tried to hide from us: fire is fun to play with. Of course, there were signs that our parents already know how great fire was: Fourth of July fireworks displays, bonfires, pyrotechnics at Metallica concerts. As fun as fire is though, your parents were right about the fact that it is dangerous.

That potential for fiery danger probably isn’t more evident than at the Burning Man festival in the Black Rock Desert of Nevada. A multitude of fire-based displays (like the titular Burning Man), dry conditions, lack of firefighting infrastructure, and a veritable cornucopia of mind-altering substances make it Smokey the Bear’s waking nightmare. Luckily for the wellbeing of everyone involved, Burning Man organizers and creators take safety very seriously.

Paul Stoffregen shows that dedication to pyrotechnic safety in his detailed log of how he built a flame sensor for a friend’s Burning Man display. Like any gas-based flame, the danger here is that the pilot light will be extinguised and gas will collect until it reaches a saturation point where it can be ignited — with explosive results. Burning Man requires these kinds of displays use pilot light sensors for just that reason.
There are a few ways to sense a flame, but Paul went with a tried and true method commonly used in gas furnaces: flame rectification. This method actually takes advantage of the electrical conductivity of a flame to sense its presence. After testing a cheap flame sensor rod with a Teensy, Paul got nice reliable measurements.

With strong signals (no ambiguity here), he tied the Teensy to a solenoid valve to control the flow of propane. The solenoid is normally closed, which means it needs power to be opened. That’s an important detail when building dangerous devices, because they need to be failsafe. A failsafe system is one that, in its inert state, is no longer dangerous. In this case, if power were to be lost completely (or if part of the system were damaged), the solenoid would close and shut off the flow of propane.
After thoroughly testing the sensor and flow control, Paul packaged everything in a nice case designed to weather the elements of the harsh Black Rock Desert. Because the art display, called Three Wishes, uses three flames, Paul built three of these fire sensor systems. Plus a spare for redundancy — yay for planning ahead!

Now the Three Wishes display is both stunning and safe! Playing with fire responsibly is the best way to play with fire. Burning Man attendees can now enjoy the pyrotechnics without worrying about the danger.


