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Hazardous Chemicals

Please read these related areas on this site: Waste Disposal and Chemical Information.

Chemicals in the organic lab can be flammable, volatile, health hazardous, and/or corrosive. In the organic chemistry lab courses at CU, we require that you know the hazards of all the chemicals in the laboratory. First and foremost, you need to know these hazards so that you will know when it is critical to take precautions such as wearing protective clothing or keeping chemicals from flame. We consider this so important that you will always be asked to look up the hazards and include them in your prelab notebook write-up, and we will put questions about chemical hazards on the prelab quizzes.

Not only does the CU Chem Department think that chemical hazard information is essential knowledge, it is a federal law (below). Whether you work in the medical field, photography, construction, retail stores, painting, etc., chemicals will be in the workplace and you have the right to know the hazards of the chemicals that are present. We hope that the lessons you learn about the hazards of chemicals will enable you to work in a safe manner whatever your future profession.

Chemical Bottle Labels

The two major systems of chemical hazard labeling are NFPA (National Fire Protection Agency) and HMIG (Hazardous Material Information Guide). Each uses the same color and number codes, but each lays the label out in a different manner:


The NPFA is concerned primarily with fire, HMIG with safety in general. Also, the manufacturer assigns the number value when they label and sell a compound, rather than the government. Therefore, number values will change from manufacturer to manufacturer according to their individual interpretation of the hazard. You can find these numbers on the MSDS for a compound.


Several different terms are used to quantify how toxic a substance is under different circumstances. These are listed below.

Term Subscript Definition Usage Description
LD Lo, 50 Lethal dose Exposure by any route except inhalation LD50 is the single dose of a toxic substance administered by any route (other than by inhalation) that causes the death of 50% of an animal population. LDLo is the lowest dose of a substance reported to have caused death in humans or animals.
LC Lo, 50 Lethal concentration Exposure by inhalation LC50 is the concentration of a material in air that kills 50% of a group of test animals when administered as a single exposure in a specific time period (usually 1 hour). LC values are often expressed as parts of material per million parts of air (ppm).
TD Lo, 50 Toxic dose Exposure by any route except inhalation TDLo is the lowest dose of a substance reported to produce any toxic effect in humans or to produce tumorigenic or reproductive effects in animals or humans. Like LD, it is used for all routes of administration except inhalation. The same subscripts, routes of administration, and species tested abbreviations are used as with LD and LC. TD50 is toxic dose 50, and means that 50% of the test subjects suffered from one or more toxic effects.
TC Lo, 50 Toxic concentration Exposure by inhalation TCLo is the lowest concentration of a substance in air to which humans (or animals) have been exposed for any given period of time that has produced any toxic effect or produced a tumorigenic or reproductive effect one or more members of the group of subjects. TC values are only for the inhalation toxicity of a compound. TC values are of great importance to industrial workers and chemists exposed to fumes and dust.
TLV TWA, STEL, C Threshold limit value Airborne concentration allowed in a normal work schedule TLV and PEL are exposure limits and are used by agencies to establish permissible exposure limits in workplaces. TLV is threshold limit value and is used by the American Conference of Governmental Industrial Hygienists (ACGIH) to express the maximum airborne concentration of a material to which most workers can be exposed during a normal daily and weekly work schedule without adverse effects. Values for TLV and PEL are usually equivalent; each is the average concentration of a chemical in the air to which most people can be exposed and show no ill effect. These values are sometimes derived from TCLo values. A PEL or TLV value refers only to inhalation toxicity, not to skin or eye contact or to ingestion. Not all TLVs have been established by scientific experimentation. Many are estimates, based on experience with the chemical or based on known information about similar chemicals. TLVs are expressed in three ways:
  • TWA is the allowable time-weighted average concentration for a normal 8-hour workday or 40-hour week to which a person can be repeatedly exposed for 8 hours a day, day after day, without adverse effect.
  • TLV-STEL is the short-term exposure limit or maximum concentration for a continuous exposure period of 15 minutes (with a maximum of four such periods per day, with at least 60 minutes between exposure periods, and provided that the daily TLV-TWA is not exceeded).
  • TLV-C is the ceiling concentration - the value not to exceeded at any time.
PEL TWA, STEL, C Threshold limit value Airborne concentration allowed in a normal work schedule PEL is the permissible exposure limit and is used by the Occupational Health and Safety Administration (OSHA). It is usually equivalent to TLV.

Some approximate toxicities are listed below. The Human Dose column lists how much compound a 150 pound adult human would have to ingest to reach the LD50.

LD50 (animal) Human Dose Toxicity Value in NFPA or HMIG
0-50 mg/kg 0-1 tsp Extreme 4
50-500 mg/kg 1 tsp to 1 oz High 3
500-5000mg/kg 1 oz to 1 pt Moderate 2
5-15 g/kg 1 pt to 1 qt Slight 1
Over 15 g/kg More than 1 qt Practically non-toxic 0

Other Hazards

The Law

The Occupational Safety and Health Administration (OSHA) requires employers to meet the requirements of the Hazard Communication Standard (HCS: 29CFR 1910.1200). The main points of this HCS as they pertain to students in the teaching labs are:

The Organic Chemistry teaching labs comply with these regulations by doing the following:

The links below will take you either to the laws on the OSHA site and to other university sites that explain these laws.