Category B

What Category B is

On this page11

The definition Which is defined against Category A The shipping name and number Which is a marking requirement, not a container one Generally capable is doing the work Most routine diagnostic samples are Category B But there is an exception and it is widely used The classification is not the shipper's convenience And the carrier has its own view What this means for a container decision References

UN3373. The definition is written as a negative.

The definition

Category B is "an infectious substance that is not in a form generally capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals when exposure to it occurs".

Which is defined against Category A

Category A is the one that is capable of that. The line between them is the seriousness of what happens on exposure, and this property does not summarize the Category A requirements because they are a different packaging instruction and a different order of care.

The shipping name and number

Described as "Biological substance, Category B" and assigned identification number UN3373. Those words and that number go on the outer packaging.

Which is a marking requirement, not a container one

The mark belongs to the outer layer of the assembly. Nothing we sell carries it or should.

Generally capable is doing the work

The definition turns on what a substance is generally capable of in a healthy person, not on what it might do in the worst case. That is a judgment, and it is made by people who assess the material rather than by a container supplier.

Most routine diagnostic samples are Category B

A specimen taken to find out whether somebody has an infection is presumed to possibly contain one, which is the ordinary case for transport purposes.

But there is an exception and it is widely used

The next page covers it: samples taken for routine testing unrelated to infectious disease diagnosis, where there is a low probability the sample is infectious.

The classification is not the shipper's convenience

It follows from what the sample is and why it was taken. Choosing the easier classification because the packaging is simpler is the failure the whole scheme exists to prevent.

And the carrier has its own view

Airlines and parcel carriers impose conditions beyond the regulation, and they are the ones who will refuse a parcel. Ask before designing the process around a shipping method.

What this means for a container decision

If the shipment is Category B, the container is one component of a tested system you should buy as a system. If it falls under the exception, the container is yours to choose and the engineering still matters.

References

49 CFR 173.134(a)(1)(ii) defines Category B as "an infectious substance that is not in a form generally capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals when exposure to it occurs", to be described as "Biological substance, Category B" and assigned identification number UN3373. Paragraph (b)(11) excepts human or animal samples transported for routine testing unrelated to the diagnosis of infectious disease where there is a low probability the sample is infectious. law.cornell.edu

49 CFR 173.199, Category B infectious substances. "A Category B infectious substance must be packaged in a triple packaging consisting of a primary receptacle, a secondary packaging, and a rigid outer packaging." Absorbent material "must be placed between the primary receptacle and secondary packaging" and "must be of sufficient quantity to absorb the entire contents of the primary receptacles". "The primary receptacle or the secondary packaging must be capable of withstanding without leakage an internal pressure producing a pressure differential of not less than 95 kPa." "The packaging must be capable of successfully passing the drop test in 178.609(d) of this subchapter at a drop height of at least 1.2 meters (3.9 feet)." "At least one surface of the outer packaging must have a minimum dimension of 100 mm by 100 mm (3.9 inches)." By aircraft, each primary receptacle may not exceed 1 L and each outer packaging 4 L for liquids, or 4 kg for solids. law.cornell.edu

Written from 49 CFR 173.199 and 173.134, and from the catalog as it stood on 19 October 2026. Nothing here is offered as a compliant primary receptacle for a regulated shipment: the pressure and drop requirements attach to a tested assembly, not to a bottle. Category A infectious substances are a different packaging instruction entirely and are not summarized. Sterility is not claimed for any product, and what a laboratory will accept is the laboratory's to say.