Why you need to wear safety glasses - Periodic Table of Videos

We have an amazing demonstration of why safety glasses are important in the lab.

It's a very simple demonstration.

Sealed tube of water heated up in front of some tomatoes.

Two of the tomatoes are wearing safety glasses, two of them are not.

We used tomatoes because tomatoes are a bit like eyeballs

and we thought it would be much too gruesome to get real eyeballs from the butcher.

When we heat one of these sealed tubes...

They're called Krakatoa tubes after the volcano that exploded catastrophically in the late 19th century.

As you heat it, the water begins to boil. Water turns into steam.

The volume of steam is much bigger than the volume of water. So the pressure goes up and up and up

and can reach several hundred atmospheres if the glass is really strong

Then suddenly

[Glass tube bursts]

and pieces of glass fly everywhere

[Glass tube bursts]

[Glass tube bursts]

[Glass tube bursts]

And if you look at the poor tomatoes.

You can see that the tomatoes without the safety glasses were pierced by pieces of glass.

One of them was actually peeled. Gives a new meaning to having your eyes peeled.

You could see where the glass had gone through the eyeball.

But like all demonstrations that we do, we thought we would do it several times.

In the second run, the glass tube wasn't strong enough and it went off with a really quite small bang.

[Glass tube bursts]

In fact, in high speed, you can see the tube flying away like a rocket.

The third tube, was an enormous explosion.

Really! Even Neil, our gallant technician, with a bit shaken.

[Glass tube bursts]

In this case, the eyeballs with the safety glasses were slightly damaged because the explosion blew the glasses up

[Glass tube bursts]

And of course, in our simulation there isn't a nose.

So, some of the glass got through the gap where you would normally have your nose.

The protecting effect of the glasses...

[Glass tube bursts]

We call them glasses they're actually made out of plastic poly-carbonate.

If you look close up, you can see where the plastic has been pitted by the flying bits of glass.

The safety glasses are probably not usable again afterwards because of the scratches.

But, you can throw those away. You can't throw away your eyeballs more than once.