An accident occurred during setup for a popular hydrogen-oxygen balloon science demonstration at a local public school. The demonstrator suffered painful second-degree burns to his right forearm and was taken to the hospital. The paramedics feared that grave respiratory damage (due to flame inhalation) might have occurred.
The demonstrator had transported 15 helium-quality balloons, pre-filled with a hydrogen-oxygen mixture, in a large, black, polyethylene garbage bag. During the setup, he opened the bag to remove a single balloon for stringing and floating. Without warning, the entire bag of balloons detonated violently. Fortunately, the incident occurred an hour prior to the program and no one else was near. It was also fortunate that only a small box caught fire and none of the other chemicals, already in place for other demonstrations, were involved.
Slow leakage of hydrogen from the balloons (since no balloon is capable of completely containing hydrogen) resulted in accumulation of hydrogen and oxygen inside the garbage bag. The dry, sealed bag created an environment ripe for the generation of static electricity. Simply touching the balloons ignited the leaking hydrogen and all 15 balloons.
Safe storage and transportation of balloons filled with a hydrogen-oxygen mixture is a very risky undertaking. There are few scenarios that do not involve enclosed spaces (e.g., a car) and the potential for static discharge. Perhaps a mesh bag would work, as long as sufficient ventilation is ensured. Nonetheless, using lecture bottles and filling balloons on-site seems to be the safest method. Yet if the floor in the demonstration area were carpeted, enough static could be generated to ignite a balloon. The demonstrator's greatest fear is that a child might ask to participate in the demonstration, then reach out to touch the balloon and have it detonate in their face.
The demonstrator feels fortunate that his injuries were relatively minor (no respiratory damage). He urges that a full risk assessment be performed prior to balloon storage/transportation and setup/performance of this type of science demonstration. Guidance for undertaking a hazard analysis and risk assessment can be found in the Hydrogen Safety Best Practices Manual.