If you sell hazmat items, it's likely that you won't offer shipping internationally to all countries. You can restrict where shipping is allowed to using MatrixDays. Because MatrixDays uses a best match approach to selecting which rules to apply there are two techniques that can be used to restrict rates depending on how you've implemented your CSV file. One is to just not define the country in your hazmat group, this will work in most scenarios.
The other option is to explicitly define the country in the group and set the shipping price in the CSV file to "-1" which means restricted. This approach reliably restricts that country but obviously can be a little more time consuming to implement if you have a lot of countries to restrict.
In the below example we ship hazmat to everywhere internationally except France and Italy.