Chapter 9: Particularly Hazardous Substances

Revised January 2023

Particularly Hazardous Substances

Carcinogens, reproductive toxins, and chemicals with high acute toxicity are considered to be high-risk materials and are classified by OSHA as “Particularly Hazardous Substances.”


In addition to chemicals classified as known carcinogens, there are many chemicals classified as “suspect carcinogens” since they show carcinogenic activity under certain circumstances but do not demonstrate unequivocal evidence of an increased risk of cancer in humans. In many cases, these suspect carcinogens are regulated by the OSHA Lab Standard as carcinogens, and in all cases, steps must be implemented to minimize exposure to these substances (see “Working with Particularly Hazardous Substances” below).

The following references provide lists of substances classified as carcinogens and suspect carcinogens; however, exclusion from this list does not guarantee that a substance does not possess carcinogenic activity.

Reproductive Toxins and Chemicals with High Acute Toxicity

Reproductive toxins are those chemicals listed as such in SDSs and other recognized sources of chemical hazard information, and highly acutely toxic chemicals are those that meet the definition of “highly toxic.” Unfortunately, there are no definitive listing of chemicals classified as reproductive toxins or highly acutely toxic, so SDSs and other sources of chemical hazard information should be consulted. One listing of chemicals known to cause reproductive toxicity is State of California's Proposition 65 list of chemicals (which also includes carcinogens)

A listing of several common laboratory chemicals that are known carcinogens, reproductive toxins, or which have high acute toxicity is provided to assist laboratory workers in identifying particularly hazardous substances. Additionally, the following lists can be used to help identify particularly hazardous substances:

Working with Particularly Hazardous Substances

Extra precaution is required when working with particularly hazardous substances. Although risk varies depending on the specific conditions of use, the procedures described in this section are generally required when handling any chemical that is a carcinogen or highly acutely toxic. Since the risk associated with reproductive toxins is highly dependent on the specific compound and the conditions of its use, these materials should be assessed on an individual basis. High risk reproductive toxins (those with unequivocal evidence of reproductive risk) should also be handled using the procedures outlined in this section.

Suspect carcinogens (check the IARC and NTP carcinogen lists above) should be handled using these procedures when using toxicologically significant quantities or under conditions with increased likelihood of exposure (such as, generation of vapor or aerosol outside of a laboratory hood, or when skin contact is likely). For the purposes of this section, a toxicologically significant quantity is an amount greater than or equal to one-half the quantity reported to produce cancer in a mammalian species, when scaled for a 50 kg (110 pound) person:

Toxicologically Significant Quantity (g) ≥ [cancer producing doce (mg/kg) x 50 kg x 1/1000] ÷ 2

Laboratory supervisors can vary these procedures based on a risk assessment of their specific application

Designated Areas

Procedures involving particularly hazardous substances that are thought to have potential for significant exposure to personnel under normal operations must be conducted in a designated area. It is recommended that procedures with lower potential for personnel exposure also be conducted in a designated area. A designated area can be the entire laboratory, a specific laboratory workbench, or a laboratory hood. The designated area is recognized as an area of increased risk where limited access, special procedures, knowledge, and work skills are required. Designated areas must be clearly marked with signs that identify the chemical hazard and include an appropriate warning; for example: WARNING! BENZENE WORK AREA – CARCINOGEN.

Procedures for Working with Particularly Hazardous Substances

Laboratory supervisors are responsible for the development of specific SOPs designed to reduce the risk associated with handling particularly hazardous substances. Although the specific SOPs will vary according to the material used, the following guidelines are generally applicable for projects involving these substances:

  • Use the smallest amount of chemical that is consistent with the requirements of the work to be performed.
  • Use containment devices (such as lab hoods or glove boxes) when: (i) volatilizing these substances, (ii) manipulating substances that may generate aerosols, and (iii) performing laboratory procedures that may result in release of the substance.
    • Use high efficiency particulate air (HEPA) filters, carbon filters, or scrubber systems with containment devices to protect effluent and vacuum lines, pumps, and the environment whenever feasible.
  • Use a ventilated containment to weigh out solid chemicals. Alternatively, the tare method can be used to prevent inhalation of the chemical. While working in a laboratory hood, the chemical is added to a pre-weighed container. The container is then sealed and re-weighed outside of the hood. If chemical needs to be added or removed, this manipulation is carried out in the hood. In this manner, all open chemical handling is conducted in the laboratory hood.
  • Use personnel protective equipment appropriate for the specific hazards when working with these substances.
    • Select chemical resistant gloves that are protective against the specific chemical(s) being used, as well as any carrier or solvent chemical.
  • Upon leaving the designated area, remove any personal protective equipment worn and wash hands, forearms, face, and neck.
  • After each use (or day), wipe down the immediate work area and equipment to prevent accumulation of chemical residue.
  • At the end of each project, thoroughly decontaminate the designated area before resuming normal laboratory work in the area.

Chapter 10: Nanomaterials