We did a little research in response to a member question about whether aircraft lavatories (lavs) should be treated as hazardous materials when shipped.
There are two different considerations in examining lavs as potential hazmats. The first is the chemicals that are found in the lavs. The second is the residual human waste that might be found in the lav.
In examining the first consideration, it is important to identify the chemicals that are used in the lav, and that remain in the lav. Most modern lavs use a non-hazardous chemical material like Blue Juice or Bio-Gem. According to the Blue Juice SDS and the Bio-Gem SDS, they are not hazmats. However, older lavs have used Formaldehyde as their chemical. Formaldehyde (and its solutions) is typically regulated as a hazmat.
Lavs are typically emptied before being shipped, but a chemical residue is usually shipped as if the chemical remains present. Therefore, when you have a hazmat-regulated chemical that was present in the lav, as long as there is a residue of that hazmat in the lav, the lav must be treated as hazmat for shipping purposes. It is not enough to empty the lav – you need to purge the chemical.
Unless it contains or is suspected to contain pathogens (Division 6.2 Infectious Substances) human waste is typically not regulated as a hazardous material under US or ICAO standards. For comparison, fecal occult blood samples are explicitly excepted from the US and ICAO definition of Infectious Substances. The US Government has explained that some of the factors behind this exception include:
These are specimens collected from healthy patients for routine testing and screening (e.g., DNA analysis, forensic studies, immunologic studies, cancer screening, and nutritional evaluations of infants, children, and adults). The specimen is placed on paper, allowed to saturate the paper, and then dried completely. The specimens pose an extremely minimal risk of infection.
In the special circumstance where you know that the lav has been exposed to specific pathogens, of course, the analysis must include and address the presence of those pathogens.
In short, before shipping the lav you should check the chemical residues in the lav. If the chemicals and/or chemical residues are hazmats, then the lav is likely shipped as a hazmat (unless the chemicalas are purged) but if they are not hazmats then the lav might not be a hazmat for shipping purposes.