One of the questions that we want in our MSDS to answer is whether something is a poison.
Let’s look at the Material Safety Data Sheet for Toluene.
At first glance this is very straightforward. If we scroll down to section 15 we see that it is a schedule 6 poison. According to the poison definitions this is a poison with moderate to high toxicity.
Seems straightforward, doesn’t it? Well, unfortunately, it doesn’t tell you much. If you scroll up to section 11 it says that it is “expected to be of low toxicity” – contradicting the S6 classification – and this is fairly common.
The poison scheduling system suffers from one major drawback – it doesn’t take concentration into account. The best example I have seen of this is with solutions of sodium cyanide. Now you don’t need to be a rocket surgeon to know that cyanide is toxic. But, as with any toxin, there is a concentration at which it ceases to be toxic.
For cyanide solutions, this concentration is about 2%. If you were to buy a solution of this stuff above 2% it would be classified as toxic under the Dangerous Goods Code, and would have a class 6 Diamond:
Below 2% however, this diamond disappears and it is classified as non-toxic.
But, unfortunately, it is still at a schedule 7 poison, and if it was labelled correctly it would have the words “DANGEROUS POISON” on it.
Also note that some of the poisons on the list are not poisons at all – schedulse 2 and 3 are medicines and schedule 4 are veterinary products.
So the definition of a poison is actually not particularly useful. The most useful information on and MSDS is the hazard classification, and the information in the toxicological section.
Tomorrow we’ll go through it in detail, and finish of the topic of chemical safety.