Last week, I watched a video on Twitter, about one of those balloons filled with Helium exploding when it reached some antennas. But, why did it explode if there is helium inside? Let’s try to figure it out.
Before that, here you get the video:
This is not an isolated case. There have been lots more.
Analysing the explosion – Theories
As you can see the explosion is quite big and overwhelming. The star-shaped balloons look made of something metallic. It’s common to see children with those in fairs. Apparently, they are made of a polymer: BoPET (biaxially-oriented polyethylene terephthalate), also called Mylar (commercial trade). Common balloons instead are made of latex. So, there are some theories that could explain this behaviour. Let’s show them:
- The first one states that the balloons weren’t filled with helium, but with hydrogen, lighter as He, but much cheaper. Hydrogen is highly reactive and could explode easily. Click on the next link to watch a Hydrogen explosion.
- The second advocates for different material composition. Some of the balloons are covered by a thin layer of aluminium.
We have set the two theories. If we think about the first one, it would be so unwise to fill it with hydrogen. Unless it was done on purpose, it doesn’t make sense. As for the second one, how could the material cause an explosion? How much does it affect?
When a metal, in this case, aluminium, hits a power line, it creates a dangerous dead short that can lead to an explosion. A dead short (also called short circuit) is caused when an electrical circuit has zero resistance. Metals are excellent electricity conductors, so when a current (in this case from a power line) touches the balloon, an outage is formed. But why did it blow up?
In a dead short, as there is no resistance, there is overcurrent in the circuit. This overcurrent can turn into an overheating of the materials (especially the poor conductive ones, like helium in our case of study). This huge amount of energy released as heat produces a fire or an explosion.
Why are Mylar balloons so abundant if they are so dangerous?
The common latex balloons, as you can imagine, are safer. However, once they are filled with any gas, they remain inflated between 8 and 12 hours on average. Whereas the Mylar balloons keep inflated for over 2 weeks. It is worthy to notice that latex balloons are 100 % biodegradable, while Mylar ones aren’t. So, taking into account all of this, BE CAREFUL with this type of balloons, especially if you are outside and if a child gets it (they are prone to fly away; the balloons, not the children :D).
About reactivity of gases: Hydrogen vs Helium
Let’s start by the beginning: hydrogen. It’s the lightest element. One molecule of hydrogen dissociates in two hydrogen atoms (H2 -> 2H), which are highly reactive. The energy of dissociation could be reached if we put some flame close, an incandescent tungsten bulb or an electrical discharge. So, the explanation of a balloon filled with hydrogen is plausible.
If you are interested in how hydrogen explodes, click on this link to watch a n explicative video with slow motion.
Helium. Helium is part of the noble gases, and as the name points out, they are noble. That means they are unreactive (Click here to get more info about the chemistry of helium).
One last question. Probably we all have lived the same with helium balloons. That moment when it takes flight from our hands since helium is so light. Have you thought about how high or far could it go? It disappears from our sight but, where did it go? It will go up until the density of the balloon (balloon + helium) will become the same as the density of the atmosphere. But remember that the temperature and pressure will change, which will affect the density of the balloon. At that moment it could explode, leak out or keep floating in the atmosphere depending on the buoyancy changes.
Hope you are now aware of the danger about balloons. If you have any comments or you want to share your experiences, please ⇓ and share!