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Highly toxic compounds have the ability to cause harmful effects, which can be local or systemic, after a single exposure. Among the most useful parameters for assessing the risk of acute toxicity of a chemical are its LD50 and LC50 values, the mean lethal dose or lethal concentration causing death in experimental animals. Per the Health Hazards Definitions of the OSHA Hazard Communication Standard, a substance is highly toxic if:

  • the oral LD50 for albino rats is less than 50 mg/kg or
  • the topical LD50 for albino rabbits is less than 200 mg/kg or
  • the LC50 in albino rats is less than 200 ppm for one hour.


A select carcinogen is a chemical agent that causes a malignant disease or statistically increases the risk of cancer, whether by initiation or promotion. Appendix 7B of the Laboratory Safety Manual lists select carcinogens that are:

  1. listed as a known or reasonably anticipated human carcinogen in the biennial Report on Carcinogens published by the National Toxicology Program
  2. listed as carcinogenic to humans (Group 1), probably carcinogenic to humans (Group 2A), or possibly carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer (IARC)
  3. regulated by OSHA as a carcinogen


A cryogen is defined as any liquid with a boiling point below 93K (-180°C or -240°F). The primary hazard of cryogenic materials is their extremely low temperature. Cryogenic materials, and surfaces they cool, can cause severe burns if allowed to contact the skin. Wear insulating gloves, eye protection, lab coat and face shield when preparing or using cryogenic liquids. Do not use liquid nitrogen or liquid air to cool a flammable mixture in the presence of air, because oxygen can condense from the air and lead to an explosion hazard.

Use insulated gloves when handling dry ice. Add dry ice slowly to the liquid portion of the cooling bath to avoid foaming over. Avoid lowering your head into a dry ice chest. Carbon dioxide is heavier than air, and suffocation can result. Do not store dry ice or liquid nitrogen in walk-in cold rooms. Carbon dioxide or nitrogen can displace and thus lower the oxygen concentration in enclosed spaces.

For more information, refer to Appendix 3-B of the Lab Safety Manual (Cryogenic Hazards).

Fact Sheets

Peroxides are chemical substances that contain the reactive peroxo unit (O22-, or R-O-O-R). Several different organic chemicals are capable of forming peroxides. Under normal storage conditions, they can form and accumulate peroxides, which may explode violently when subjected to thermal or mechanical shock. This can occur even when the containers appear to be tightly closed.


Reproductive Toxin Vessel LabelReproductive toxins are defined by the OSHA Laboratory Standard as substances that cause chromosomal damage (mutagens) and/or substances with lethal or teratogenic (malformation) effects on fetuses. These can include chemicals, biologicals, and radioactive materials. Chapter 8 of the Laboratory Safety Manual outlines the proper precautions, postings, procedures and controls when working with reproductive hazards.

Examples of reproductive toxins commonly found in laboratories include:

  • 1,3-Butadiene
  • Arsenic
  • Benzene
  • Cadmium
  • Carbon disulfide
  • Dibromochoropropane
  • Ethylene dibromide
  • Ethylene glycol monomethyl (and ethyl) ethers
  • Ethylene oxide
  • Ethylene thiourea
  • Fluorouracil (5-FU)
  • Ionizing radiation
  • Lead
  • Mercury compounds
  • Polychlorinated biphenols (PCBs)
  • Tamoxifen
  • Toluene
  • Urethane

UNC-Chapel Hill is committed to providing additional protection for the conceptus and to establish specific procedures to protect pregnant employees. Review Chapter 8 of the Laboratory Safety Manual for more information regarding the University’s Conceptus Protection Program. If you wish to take advantage of the program, contact EHS as soon as possible after determining or contemplating pregnancy.


Additional Chemicals, Hazards and Substances

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