Hazmatlaw provides a conceptual summary of the different hazard classes found in the HMR. At most, these summaries can be used as a “primer” for understanding the hazard class definitions as set forth by DOT in the HMR, and certainly not as a substitute. At the bottom of each classification summary is a link to the regulations themselves titled, "Check The Regs."
The sample hazmat items listed in the summaries are illustrative only -- there are thousands of specifically listed hazmat items in the HMR, and many more unlisted items qualify as hazmat because of their physical characteristics.
The HMR generally define explosives to be “any substance or article, including a device which is designed to function by explosion (i.e., an extremely rapid release of gas and heat) or which, by chemical reaction within itself, is able to function in a similar manner even if not designed to function by explosion.” 49 CFR §173.50(a).
There are six divisions for Class 1 materials, divided on the basis of the type and severity of possible explosion (i.e. from Division 1.1, a mass explosion hazard to Division 1.6, which applies to very insensitive explosive articles that do not present mass or projective explosion risks). Some, but not all types of explosives are forbidden from air transportation.
The following are some examples of Class I hazmat: Certain types of air bag
inflators, ammunition, gun powder, water-activated contrivances, sounding devices,
distress signals, rocket engines, liquid propellant, various primers, jet fuel,
fire works, and safety fuses. 49 CFR § 172.101. The HMR also specifies
certain explosives that are forbidden from being offered for commercial transportation.
49 CFR § 173.54.
There are three types of gases that qualify as hazmat – flammable gas, poisonous gas, and compressed gas. 49 CFR § 173.115. A gas is flammable when it is either ignitable or flammable when mixed with air under certain conditions. 49 CFR §173.115(a). Examples of flammable gas include: certain aerosol products, engine starting fluids, butane, certain refrigerant gases, propane, dissolved acetylene and cigarette lighters. 49 CFR § 172.101.
A gas is poisonous when it is either known or presumed to be toxic enough to pose a health hazard to humans during transportation. 49 CFR §173.115(c). Examples of poisonous gas include: carbon monoxide, chlorine, nitric oxide, hydrogen bromide, and anhydrous ammonia. 49 CFR § 172.101.
Compressed gas is gas that is neither flammable nor poisonous, but is packaged
in a manner so that the absolute pressure is 40.6 pounds per square inch (absolute)
or greater. 49 CFR §173.115(b). Compressed gas includes liquefied gas,
pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing
gas. Id. Examples of compressed gas include: numerous household aerosol products,
compressed air, and airbag inflators. 49 CFR § 172.101.
There are no hazard category subdivisions in Class 3, and the number of materials that qualify as flammable liquid is quite large. The HMR generally define flammable liquids as a “liquid having a flashpoint of not more than 60.5° C (141° F), or any material in a liquid phase with a flashpoint at or above 37.8° C (100° F) that is intentionally heated and offered for transportation or transported at or above its flashpoint in a bulk packaging.” 49 CFR §120(a). The method for determining flashpoint is specified in the HMR. 49 CFR §120(c).
Class 3 also includes combustible liquids, which are defined as any liquid that does not meet the definition of any other hazard class and has a flashpoint above 60.5° C (141° F), but below 95° C (200° F). Under certain circumstances, combustible liquids can be excluded from regulation under the HMR.
Examples of Class 3 flammable liquids can include: gasoline, diesel fuel, kerosene,
crude oil, certain alcoholic beverages and flavoring oil extracts, cleaning
liquid compounds methanol, paint and a variety of paint-related products, adhesives,
benzene, camphor oil, certain medicines and rosin oil. 49 CFR § 172.101.
Class 4 -- Flammable Solids, Spontaneously Combustible Material, and Material that is Dangerous When Wet
As a general matter, there are three types of materials that qualify as flammable solids: (1) certain types of desensitized explosives; (2) certain self-reactive materials (materials that are thermally unstable and can undergo a strongly exothermic decomposition without air); and (3) readily combustible materials such as certain metal powders, or materials that can cause fire through friction (such as matches) or that have an accelerated burn rate. 49 CFR §173.124(a).
The HMR designates seven different self-reactive material types, Type A through Type G, in descending order of hazard risk presented, with Type A being banned from commercial transportation. 49 CFR §173.124(a)(2)(E). Matches and coated aluminum powder are examples of Class 4.1 (flammable solids) material.
There are two types of spontaneous combustible material -- pyrophoric material and self heating material. 49 CFR §173.124(b). Pyrophoric material is a liquid or solid that can, without an external ignition source, ignite within five minutes of coming into contact with air. 49 CFR §173.124(b)(1). A self heating material is a material that, when in contact with air and without an energy supply is liable to self heat. 49 CFR §173.124(b)(2). Certain nitrocellulose-based self-healing plastics, for example, qualify as 4.2 spontaneous combustible material. 49 CFR § 172.101.
Material that is dangerous when wet, Class 4.3, means material that by contact
with water is liable to become spontaneously flammable or give off a flammable
or toxic gas at a rate greater than 1 liter per kilogram of the material per
hour. 49 CFR §173.124(c). Many raw elements, such as lithium, potassium,
barium and calcium, qualify as a Class 4.3 dangerous when wet material. 49 CFR
§ 172.101.
Class 5 -- Oxidizers and Organic Peroxides
Under the HMR, oxidizers are materials that may, generally by yielding oxygen, cause or enhance the combustion of other materials. 49 CFR §173.127(a). Both solids and liquids can qualify as oxidizers, and the HMR specifies test procedures to determine whether a material qualifies as an oxidizer. 49 CFR §173.127(a)(1). Ammonia nitrate fertilizer and lead nitrate are examples of Class 5.1 oxidizers. 49 CFR § 172.101.
The HMR generally defines organic peroxides to be any organic compound containing
oxygen in the bivalent O-O structure and which may be considered a derivative
of hydrogen peroxide, where one or more of the hydrogen atoms have been replaced
by organic radicals. 49 CFR §173.128(a). There can be some overlap between
qualifying as a Class 5.2 organic peroxide and a Class 1 explosive, and when
this occurs the material generally must be classified as a Class 1 explosive.
49 CFR §173.128(a)(1). The HMR designates seven different organic material
types, Type A through Type G, in descending order of hazard risk presented,
with Type A being banned from commercial transportation. 49 CFR §173.128(b).
Class 6 -- Poisonous Materials and Infectious Substances
The HMR defines poisonous material as any material, other than a gas which is known to be so toxic to humans as to afford a hazard to heath during transportation, or if the material is presumed to be toxic to humans because of animal testing with respect to oral toxicity, dermal toxicity, or inhalation toxicity. 49 CFR §173.132(a).
Arsenic, arsenic compounds, copper-based pesticides, tear gas, anti-knock compounds, trichloroethylene, and 1,1,1-trichloroethane are examples of Class 6.1 poisonous materials. 49 CFR § 172.101.
The biohazard materials from Class 6.2 include infectious substances, diagnostic
specimens, biological products, and regulated medical wastes. 49 CFR §173.134(a).
There are a number of exceptions and exclusions associated with Class 6.2, and
in some cases compliance with Occupational Safety and Health Administration
(OSHA) regulations can be substituted for compliance with the HMR. 49 CFR §173.134(b).
Class 7 -- Radioactive Materials
The HMR defines radioactive materials as any material having a specific activity
greater than 70 Becquerel (Bq) per gram. 49 CFR §173.403. The specific
activity of a radionuclide is the activity of the radionuclide per unit mass
of that nuclide. Id. The specific activity of a material in which the radionuclide
is essentially uniformly distributed is the activity per unit mass of the material.
Id. Articles or instruments, such as clocks, electronic tubes or apparatus that
have radioactive material in gaseous or solid, non-dispersible solid form as
a component part of the article or instrument are subject to regulation as Class
7 radioactive materials. Id. There are, however, fairly broad exceptions for
articles or instruments containing radioactive material as a component part
when certain packaging formats are used, and certain radiation measurements
can be satisfied. 49 CFR §173.424.
Class 8 -- Corrosive Materials
Liquids or solids that cause full thickness destruction of human skin at the
site of contact within a specified time period, and liquids that can have a
severe corrosion rate on steel or aluminum qualify as Class 8 corrosive materials
under the HMR. 49 CFR §173.136(a). Numerous industrial and consumer products
qualify as Class 8 corrosive items, including certain wet and dry batteries
and alkali battery fluid, certain dyes, formic acid, hydrochloric acid, nitric
acid, mercury and devices containing mercury (such as thermometers and electron
tubes). 49 CFR § 172.101.
Class 9 -- Miscellaneous Hazardous Material
Material that presents a hazard during transportation but which does not meet
the definition of any other hazard class is classified under the HMR as Class
9 material. 49 CFR §173.140. Class 9 material includes any material which
has an anesthetic, noxious, or other similar property which could cause extreme
annoyance or discomfort to a flight crew member so as to prevent the correct
performance of assigned duties; or any material that meets the HMR definition
for elevated temperature materials, a hazardous substance, or a marine pollutant.
Id. As a “catch-all” category, Class 9 covers a wide spectrum of
products and materials, including: battery-powered vehicles and equipment (including
electric wheelchairs), dangerous goods in machinery (such as fuel system components),
first aid kits, asbestos, and plastic molding compound. 49 CFR § 172.101.
ORM -- Other Regulated Materials
Under the HMR, the term “Other Regulated Material” (ORM) means a material, such as a consumer commodity, which, although otherwise subject to the HMR, presents a limited hazard during transportation due to its form, quantity and packaging. 49 CFR §173.144. For a material to qualify as ORM, it must be specifically listed in the §172.101 hazmat table.
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