Nova Scotia·Q&A

Could old rubbing alcohol be a household hazard? That depends, says Dal prof

After Halifax Regional Police blew up a bottle of rubbing alcohol earlier this week, CBC spoke to a Dalhousie chemistry professor about how the chemical could have solidified and how commonly it happens.

'The best practice for laboratory chemicals that have gone off is to detonate them, like the police did'

Halifax Regional Police had to detonate an expired bottle of rubbing alcohol earlier this week. (Shutterstock/Octavian Lazar)

A chemistry professor in Halifax says he was surprised to learn that rubbing alcohol had solidified when Halifax Regional Police blew up the expired household chemical on Wednesday.

Alex Speed, assistant professor of chemistry at Dalhousie University, said in order for isopropyl alcohol, or isopropanol, to solidify, it would have to meet specific criteria.

Police were called to an apartment building on Tower Road around 10:30 p.m. to a report of a "volatile substance" earlier this week.

The forensic identification unit believed the substance was too unstable to transport and opted to detonate it outside the building.

Halifax Regional Police would not comment further on Friday, other than to say the substance "was quite old" and the owner believed it may require a proper disposal.

Speed spoke to the CBC about the incident and whether people should worry about the rubbing alcohol in their own homes.

Why would the police have to detonate expired rubbing alcohol?

If you have a substance like an ether that has crystals and peroxides in it, it can become a shock-sensitive hazard. So if it's exposed to mechanical forces, which could even include opening a bottle, it could potentially explode.

So that is the best practice for laboratory chemicals that have gone off is to detonate them, like the police did.

How does something like rubbing alcohol turn into a solid?

It is possible for organic solvents [isopropanol is one of them] to undergo a process called oxidation, which makes something called peroxides. This is a very similar process to what happens when cooking oil in the kitchen goes rancid.

But you would need a very specific set of conditions. It would have to be exposed to air, it would have to be exposed to bright light and this would have to go on for quite a long time without the alcohol actually evaporating.

While there have been some cases where people have had isopropanol or rubbing alcohol that has formed peroxides, in none of those cases was it ever reported that they were solids.

So it's possible that there was something else in the rubbing alcohol, like maybe a fragrance or a soap, that could be left behind if some of the alcohol evaporated and would leave behind a solid residue.

Isopropyl alcohol is a flammable substance. (Jennifer Beanlands)

How long would the bottle have to be sitting there for this to happen?

The reading that I did where people in labs had encountered problems with isopropanol, the bottles had been sitting for years. So on the order of 10 years, 15 years. I think in one case it was four years. And there was typically bright light like sunlight involved also.

If it was sealed properly it would not be able to form peroxides. For the entire bottle of isopropanol to react, you would need hundreds of litres of air to enter, which wouldn't be possible through a sealed lid.

What's more dangerous is if you have a bottle of a solvent it's half full. The amount of air that's left in the top half of a bottle, what we would call the head space, could be enough to form peroxides that … would be dangerous if the solvent was concentrated.

Should people be worried about the rubbing alcohol in their home?

I'll be frank, when I read about it in the news the morning it happened, I was very surprised. I probably have about 16 litres of isopropanol in my lab. I have never in my career encountered this happening before.

So I think people who have a bottle of rubbing alcohol in their medicine cabinet shouldn't be concerned that it has suddenly turned into something that's going to explode on them.

I think if people are worried about rubbing alcohol, the main thing to actually take away is regardless of whether it has gone bad or not, it is a flammable substance. And it could catch on fire if it were spilled next to an open flame — and that would be something far more common than any kind of peroxide formation.

As far as disposal goes, some things online might tell you it's safe to go down the sink. That's actually not right, that's against the Halifax wastewater bylaws. But HRM has a program for household special waste that would accept chemical waste generated in the home.

Are there other household chemicals that people should keep an eye on or be aware of this happening?

The only one I would say is that some people might have diethyl ether in their garage as an engine starter. That usually comes in a can that is protected from air, but that would be far more dangerous.

It's important that people realize that a lot of common household chemicals are things that should be treated with respect.

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