Particularly Hazardous Substances - University of Houston
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Particularly Hazardous Substances

Laboratories at UH should evaluate Safety Data Sheets (SDS) and shoud treat chemicals as particularly hazardous substance (PHS) if they have one or more hazard classification indicated below. If the chemical has a hazard classification shown with * in the below table, it is also considered "high risk" PHS.

UH EHS has developed chemical SOP templates and guidelines which the PIs can choose to adopt or develop their own with the mininum safety elements addressed.

Particularly Hazardous Substance (PHS) 


Select Carcinogens 

Any substance that meets at least one of the following criteria: 

  • GHS Carcinogenicity, Category 1A or 1B or; 
  • Regulated by OSHA as a carcinogen or; 
  • Listed under the category, "known to be carcinogens," in the Annual Report on Carcinogens published by the National Toxicology Program (NTP) or; 
  • Listed under Group 1 ("carcinogenic to humans") by the International Agency for Research on Cancer (IARC) Monographs or; 
  • Listed in either Group 2A or 2B by IARC or under the category "reasonably anticipated to be carcinogens " by NTP.

Reproductive Toxins 

Chemicals that affect the reproductive capabilities including causing chromosomal damage (mutations) and adverse effect on fetal development (teratogenesis), include those listed as:

  • GHS Reproductive Toxicity, Category 1A or 1B.

Acute Toxicity 

The ability of a chemical to cause a harmful effect after a single exposure. Chemicals having high acute toxicity include the following GHS classifications:

  • Acute Toxicity by Inhalation or Dermal Exposure, Category 1* or 2;
  • Acute Toxicity by Oral exposure, Category 1.

Specific Target Organ Toxicity (Single Exposure) (STOT-SE) 

Specific target organ toxicity (single exposure) (STOT-SE) means specific non-lethal effects on organs or organ systems in the body following single exposure to a chemical. All significant health effects that can impair function, whether reversible or irreversible, occurring immediately after exposure or following a delay. Chemicals having STOT-SE Categories 1 include the following GHS classification:

  • Specific Target Organ Toxicity - Single Exposure, Category 1.

Respiratory Sensitizer 


Respiratory Sensitizer is a substance that will lead to hypersensitivity of airways following inhalation of the substance. Chemicals having Respiratory Sensitizer Categories 1 include the following GHS classification:

  • Respiratory Sensitizer, Category 1.

Reactive & Explosive Chemicals 

Reactive & explosive chemicals considered Particularly Hazardous (and High Risk*) include the following GHS and UN classifications:

  • Oxidizing liquid or solid, Category 1.
  • In contact with water releases flammable gas, Category 1 or 2.
  • In contact with acids liberates (very) toxic gas.
  • In contact with water liberates toxic gas.
  • Reacts violently with water*.
  • Pyrophoric liquid or solid, Category 1*.
  • Pyrophoric gas*.
  • Explosives, Unstable or Divisions 1.1 - 1.3*.
  • Explosive when dry, or Explosive with or without air contact*.
  • Self-reactive or Organic peroxides, Type A* or B.
  • Self-heating, Category 1*.