Chapter 15: Communication of Chemical Hazards

Revised January 2020

Classification of Chemical Hazards

Specific criteria has been established by OSHA for the classification of health and physical hazards, with many hazard classes sub-divided into hazard categories based on the severity of the hazard. The following tables summarize the health and physical hazards to be considered when classifying a chemical.

Health Hazard Classification (see OSHA chemical health hazard criteria)
Hazard Class Hazard Category
Acute Toxicity: oral, dermal, inhalation 1, 2, 3, 4
Skin Corrosion/Irritation 1A, 1B, 1C,, 2 (irrit)
Serious Eye Damage/Irritation 1, 2A (irrit), 2B (irrit)
Respiratory/Skin Sensitization 1A, 1B
Germ Cell Mutagenicity 1A, 1B, 2
Carcinogenicity 1A, 1B, 2
Reproductive Toxicity 1A, 1B, 2, lactation
Specific Organ Toxicity – single exposure 1, 2, 3
Specific Organ Toxicity – repeated exposure 1, 2
Aspiration Hazard 1
Simple Asphyxiants Single category
Physical Hazard Classification (see OSHA chemical physical hazard criteria)
Hazard Class Hazard Category
Explosives Unstable Explosives, Div. 1.1, Div. 1.2, Div. 1.3, Div. 1.44, Div. 1.5, Div. 1.6
Flammable Gases 1, 2
Flammable Aerosols 1, 2
Oxidizing Gases 1
Gases Under Pressure None
Compressed Gases Single category
Liquefied Gases Single category
Refrigerated Liquefied Gases Single category
Dissolved Gases Single category
Flammable Liquids 1, 2, 3, 4
Flammable Solids 1, 2
Self-Reactive Substances Type A, Type B, Type C, Type D, Type E, Type G
Pyrophoric Liquids 1
Pyrophoric Solids 1
Self-Heating Substances 1, 2
Chemicals Which, In Contact With Water, Emit Flammable Gases 1, 2, 3
Oxidizing Liquids 1, 2, 3
Oxidizing Solids 1, 2, 3
Organic Peroxides Type A, Type B, Type C, Type D, Type E, Type G
Corrosive to Metals 1

Hazard Ratings

The hazard categories provide information on the severity of the hazard, with some categories including numerical ratings. Under the Hazard Communication Standard (HCS) criteria, the highest hazards are rated as “1” and lower hazards are rated as successively higher numerical or alphabetic ratings. This hazard rating scheme is in contrast to the commonly used National Fire Protection Association (NFPA) 704 and Hazardous Materials Identification System (HMIS) systems which use a hazard rating of “0” for the lowest hazard and “4” for the highest hazard. A comparison of the HCS hazard rating scheme and the NFPA 704 and HMIS schemes is shown below.

NFPA/HMIS Hazard Ratings
Rating Degree of Hazard
0 Minimal Hazard
1 Slight Hazard
2 Moderate Hazard
3 Serious Hazard
4 Severe Hazard
HCS Hazard Ratings
Rating Degree of Hazard
Category 5 Minimal Hazard
Category 4 Slight Hazard
Category 3 Moderate Hazard
Category 2 Serious Hazard
Category 1 Severe Hazard

Hazard Definitions

The HCS hazard definitions may differ from other commonly used definitions. Of particular note is the use of the term “flammable liquid.” The International Fire Code (IFC) and the NFPA classify liquids with flash points of less than 100 °F as a flammable liquid, with liquids having flash points greater than 100 °F as combustible liquids. The HCS classifies flammable liquids as those with a flash point of less than or equal to 200 °F.

IFC/NFPA flammable liquid = flash point < 100 °F (38 °C)

HCS flammable liquid = flash point ≤ 200 °F (93 °C)

Safety Data Sheets

Safety Data Sheets (SDSs) are chemical hazard information sheets designed to provide users with the information necessary to handle the chemical safely. OSHA regulations require that chemical manufacturers and vendors supply MSDSs to chemical users, and that workers have ready access to SDSs.

  • All SDSs received with incoming hazardous chemicals must be retained.
  • A SDS is not required for uncharacterized research material used only by the laboratory that produced it, or for laboratory reagents mixed in the laboratory; however, laboratory workers must be aware of the hazards presented by these chemicals. If the hazards are unknown the chemical must be handled in a manner to minimize exposure to personnel.
  • If a chemical substance is prepared for another user outside of the laboratory, the requirements of the OSHA Hazard Communication Standard (29 CFR 1910.1200) must be met, including preparation of a SDS. Contact EH&S for assistance with preparation of SDSs.

SDS Review and Availability

Before using a new chemical, laboratory workers should review the SDS. Consequently, all laboratory workers must know the location of the SDSs that are maintained by the laboratory, and how to obtain SDSs covering additional chemicals used in the laboratory.

  • Copies of many SDSs are forwarded to EH&S by chemical vendors. These SDSs can be accessed from the EH&S SDS Database.
  • EH&S subscribes to an electronic database that includes SDSs and other sources of chemical hazard information. The database is available to the UNR community (via campus computers only) through the EH&S web site as follows:
  • Additional sources of SDSs:

Additional Hazard Information

Since SDSs may not always provide adequate chemical hazard information and do not cover non-chemical hazards, additional sources of hazard information must be available to laboratory workers. The UNR libraries have multiple resources available that discuss laboratory hazards. The following are widely used laboratory safety references that are available at UNR libraries:

Note: older editions of this reference are available from UNR libraries.

Chemical Labeling

Unidentified chemicals represent an increased risk to personnel due to a lack of information on how to properly handle the material. Additionally, unknown chemicals may be a financial burden since they cannot be disposed of without identification, which may involve laboratory analysis. To avoid unidentified chemicals, label all chemical containers as described below.

Original Manufacturer’s Containers

OSHA regulations require that manufacturers’ chemical labels include the following information:

  • Product Identifier: The name of the chemical or chemical product.
  • Signal Word: Used to indicate the relative severity of the hazard. Only “Danger” or “Warning” can be used, with “Danger” indicating more severe hazards and “Warning” indicating less severe hazards.
  • Pictogram: Any number of the eight pictograms shown below will be used to display the major hazard categories associated with the chemical. When a chemical has multiple hazards, different pictograms will be used to display the various hazards.
  • Hazard Statements: Describe the nature of the hazards associated with the chemical. All applicable hazard statements must appear on the chemical label. Hazard statements should be consistent regardless of the chemical or manufacturer.
  • Precautionary Statements: Describe recommended measures to prevent adverse effects that may result from exposure to the chemical. When there are similar precautionary statements, the statement providing the most protective information will be listed.
  • Name, Address, and Phone Number: The name, address, and phone number of the chemical manufacturer or distributor.

Additional regulations require that:

  • Labels on manufacturers’ containers must not be removed or defaced unless the container has been emptied or the chemical corresponding to the original label has been replaced with a different chemical.
  • If the original label is missing or is illegible, it must be replaced with a label containing the above information.

Chemical Hazard Pictograms

The following chemical hazard pictograms are required by OSHA to be included on manufacturers’ chemical labels. Chemical labels will include multiple pictograms as is needed to communicate all hazards associated with the particular chemical.

Health Hazard

  • Carcinogen
  • Mutagenicy
  • Reproductive Toxicity
  • Respiratory Sensitizer
  • Target Organ Toxicity
  • Aspiration Toxicity

An icon depticting a human silhouette behind a six-pointed stellar shape.


  • Flammables
  • Pyrophorics
  • Emits Flammable Gas
  • Self-Reactivates
  • Organic Peroxides

An icon depicting a flame.

Exclamation Mark

  • Irritant (skin and eye)
  • Skin Sensitizer
  • Accute Toxicity (harmful)
  • Narcotic Effects
  • Respiratory Tract Irritant
  • Hazardous to Ozone Layer(non mandatory)

An icon depicting an exclamation mark.

Gas Cylinder

  • Gases Under Pressure

An icon depicting a cylinder or bottle.


  • Skin Corrosion/burns
  • Eye Damage
  • Corrosive to Metals

An icon depicting a corroding material.

Exploding Bomb

  • Explosive
  • Self-Reactives
  • Organic Peroxides

An icon depicting an exploding object.

Flame over Circle

  • Oxidizers

An icon depicting a circle in front of a flame.

Environment *(Non Mandatory)

  • Aquatic Toxicity

An icon depicting a tree and a stream.

Skull and Crossbones

  • Acute Toxicity (fatal or toxic)

An icon depicting a skull and crossbones.

Secondary Containers

Chemicals that are transferred from their original container to a secondary storage container and which will be stored long term must be labeled to indicate the chemical name, and the primary hazards should be indicated through use of the above pictograms or hazard wording. Likewise, containers of chemical mixtures that have been prepared in the laboratory for use as reagents (such as buffers, or dilute acid or base solutions) must be labeled to indicate the hazardous chemical constituents and the primary hazards should also be indicated. Include chemical concentrations on reagent containers (such as acids and bases) to accurately communicate the hazards associated with the material. The chemical name and hazard information must be consistent with the original manufacturer’s label.

Where practical, chemical names must be spelled out on container labels. Abbreviations and common reagent names may be used for labeling provided that information on the chemical constituents is available in the laboratory, and laboratory personnel are familiar with this information.

Temporary chemical containers (such as beakers, volumetric flasks, and reaction vessels) in active use require only a content identifier label; however, hazard warnings are recommended for reagents that are highly toxic, highly flammable, or which have other significant hazards. If these containers are stored they should also be labeled to indicate the primary hazards.

Research Materials

The hazards of chemicals synthesized in the laboratory, and other research materials, are often not completely known and complete hazard labeling is not possible. Nevertheless, research materials must be labeled as completely as possible using the following guidelines:

  • Label research materials with the name of the responsible researcher and the identity and hazards (as available). General labeling to indicate chemical identity or class of chemical and hazards can be used when specific information is not known or cannot be included on labels in a practical manner (e.g., a large number of containers of research materials in process).
  • References to research notebooks, etc. should be included when necessary to convey identity and hazard information.

Chemical Delivery Systems

Inadequate labeling of chemical piping and tubing delivery systems can confuse personnel and lead to chemical exposure, fire, or explosion due to inadvertent cutting of lines or unsafe work practices (such as use of flame near lines containing a flammable chemical).

  • All facility piping used for delivery of natural gas, water, and air must be labeled with content identifier labels placed periodically along the length of the delivery system.
  • Non-facility delivery systems to include semi-permanent and temporary piping or tubing of compressed gases or other chemicals must also be labeled throughout the delivery system.