(Please tell us how to determine the PSN for organic peroxides.)

Q.
The shipper made a DGD stating UN 3103 Organic peroxide Type C, liquid (Tert-butyl peroxybenzonate 80%, Cumyl hydroperoxide 20% mixture) . Referring to Appendix C.2, both Tert-butyl peroxybenzonate as well as Cumyl hydroperoxide are listed. Please tell us why did the shipper assign the material to UN 3103. (30 Jun 12)

A.
By referring to Table C.2, we see Tert-Butyl peroxybenzonate 80% will fall under Concentration 77-100 and therefore should be assigned to UN 3103.

For mixtures, the clue for determination will be for the larger component. When you look for Cumyl hydroperoxide 20% in Table C.2, you will find that since the Concentration is less than 90%, it should be assigned to UN 3109. Thence, Note 18 applies and a Corrosive subrisk label becomes unnecessary.

Now, looking at the blue pages, you will see that the PSN for UN 3103 is Organic peroxide Type C, liquid ★ and the PSN for UN 3109 is Organic peroxide Type F, liquid ★. Type A is too dangerous and cannot be carried, and Type G is not restricted. In this instance, you will consider the larger percentage component, the younger letter (i.e., degree of danger), and you come to a conclusion that the substance must be Dec ared as UN 3103 Organic peroxide Type C, liquid (Tert-Butyl peroxybenzonate 80%, Cumyl hydroperoxide 20%). As you can see from the blue pages, even if you use the same PI 570, the quantity permitted for Type C is less than that permitted for Type F, i.e., the degree of danger is higher.

Still however, when assigning PSN to a mixture, you should not determine by the characteristics of each component, but it is necessary to consider the substances as a mixture since a chemical reaction May take place by mixing them. You will have no other recourse but to refer to the MSDS.


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