Classification and packing groups

Classification is the first and most important decision in any hazmat shipment. It decides the hazard class and division, any subsidiary hazard, the packing group, the identification number and proper shipping name, and through them every other requirement: the packaging, the labels and placards, the shipping paper, the emergency response information and the exceptions that may apply. Under 49 CFR 173.22, the shipper (the person who offers the material for transport) is responsible for classifying it correctly, and the shipper's certification on the shipping paper declares that the material is properly classified, described, packaged, marked and labeled.

Where classification information comes from

Most shippers do not run laboratory tests themselves. They rely on the manufacturer's classification, which normally appears in section 14 (transport information) of the safety data sheet, introduced in HSE-102. That is a reasonable starting point, but it is not a guarantee. Safety data sheets can be out of date, written for another country, or wrong. If you change a product by diluting it, mixing it with something else or using it and shipping the waste, the original classification may no longer apply. When in doubt, check the regulations' criteria or ask the manufacturer or a qualified dangerous goods specialist.

The HMR do not require a general classification report for every product, but the shipper must be able to support its classification, and PHMSA inspectors may ask how a product was classified. Some materials, such as self-reactive substances, organic peroxides and explosives, need specific approvals or test data. After Lac-Mégantic, rules were added requiring sampling and testing programs for unrefined petroleum products such as crude oil, with records kept and made available to the Department of Transportation.

Listed by name or described generically

There are two ways a product can be identified. Some products are listed by name: gasoline, acetone, propane, sulfuric acid. If your product is exactly that substance, you use the name, class and packing group given in the list. Other products are mixtures or substances without their own entry. These are assigned to a generic or not otherwise specified entry, abbreviated N.O.S., such as Flammable liquid, N.O.S. or Corrosive liquid, acidic, organic, N.O.S. Generic entries require you to work out the class and packing group from the product's properties, and many of them require the technical name of the hazardous component in brackets on the shipping document so that responders know what they are dealing with.

Choosing the most specific entry that fits is a rule, not a preference. If an entry exists for the exact substance, use it. If not, use the most specific generic entry, for example Alcohols, N.O.S. rather than Flammable liquid, N.O.S. Lesson 5 explains how entries are chosen from the list.

Packing groups

Packing groups rank the degree of danger within classes 3, 4, 5.1, 6.1, 8 and 9: packing group I for great danger, II for medium danger and III for minor danger. Packing groups do not apply to class 2 gases, class 7, division 6.2 or most of class 1, which have their own systems. The packing group decides how strong the packaging must be, how much can be shipped as a limited quantity, and in some cases whether an emergency response assistance plan or special handling is needed. Packing groups are written in Roman numerals on documents, sometimes preceded by PG.

Flammable liquids

For class 3, two measurements decide the packing group: the flash point and the initial boiling point, the temperature at which the liquid starts to boil.

Toxic substances

For division 6.1, the packing group comes from the substance's toxicity, measured in animal studies or estimated from the toxicity of its components. Three routes are considered: swallowing (oral LD50, the dose that kills half of test animals, in milligrams per kilogram of body weight), skin contact (dermal LD50) and breathing dusts or mists (inhalation LC50, in milligrams per liter of air). The most severe result decides the packing group.

Corrosives

For class 8, the packing group depends on how fast the substance destroys skin. Packing group I substances cause full-thickness destruction of skin within an observation period of 60 minutes after an exposure of 3 minutes or less. Packing group II substances do so after an exposure of more than 3 minutes up to 60 minutes. Packing group III substances do so after an exposure of more than 60 minutes up to 4 hours, or corrode steel or aluminum at more than 6.25 mm a year. Modern classification uses validated test methods that do not require animal testing for many products.

Other classes

Classes 4 and 5.1 have packing group criteria based on burning rates and other test results described in the UN Manual of Tests and Criteria. Organic peroxides (5.2) and self-reactive substances (4.1) are assigned to types A to G instead. Some class 9 entries have packing groups II or III. Gases are classified by flammability, toxicity and pressure. Radioactive materials are classified by activity and form.

# Assigning packing groups from test data (simplified from the criteria tables).
def pg_class3(flash_c, ibp_c):
    if flash_c > 60:
        return "not class 3 (unless shipped hot)"
    if ibp_c <= 35:
        return "PG I"
    return "PG II" if flash_c < 23 else "PG III"

def pg_toxic(oral=None, dermal=None, dust=None):
    limits = {"oral": (5, 50, 300), "dermal": (50, 200, 1000), "dust": (0.2, 2, 4)}
    results = []
    for route, value in (("oral", oral), ("dermal", dermal), ("dust", dust)):
        if value is None:
            continue
        a, b, c = limits[route]
        results.append(1 if value <= a else 2 if value <= b else 3 if value <= c else 9)
    best = min(results)
    return "not 6.1 by these routes" if best == 9 else "PG " + "I" * best

for name, fp, bp in [("ether", -45, 35), ("gasoline", -43, 39), ("acetone", -20, 56),
                     ("kerosene", 43, 150), ("diesel", 52, 180), ("glycol", 111, 197)]:
    print(f"{name:>9}: flash {fp:>4} C, boil {bp:>3} C -> {pg_class3(fp, bp)}")
print("pesticide A (oral 30, dermal 400):", pg_toxic(oral=30, dermal=400))
print("pesticide B (oral 600, dust 1.5):  ", pg_toxic(oral=600, dust=1.5))
print("cleaner C (oral 2500):             ", pg_toxic(oral=2500))

    ether: flash  -45 C, boil  35 C -> PG I
 gasoline: flash  -43 C, boil  39 C -> PG II
  acetone: flash  -20 C, boil  56 C -> PG II
 kerosene: flash   43 C, boil 150 C -> PG III
   diesel: flash   52 C, boil 180 C -> PG III
   glycol: flash  111 C, boil 197 C -> not class 3 (unless shipped hot)
pesticide A (oral 30, dermal 400): PG II
pesticide B (oral 600, dust 1.5):   PG II
cleaner C (oral 2500):              not 6.1 by these routes

Observe that pesticide B is not toxic enough by mouth to be regulated, but its dust is harmful enough to inhale that it lands in packing group II. Every route must be checked, and the worst one wins.

Mixtures, solutions and wastes

A mixture or solution containing a listed substance is not automatically classed the same as the pure substance. A dilute solution may fall into a less severe packing group or out of the regulations altogether, while a mixture of two hazardous substances may need a different entry. The safety data sheet for the mixture should give its transport classification; if you prepared the mixture yourself, you must classify it. Wastes are classified the same way as products, based on their properties, and are usually shipped under the entry that fits their hazards with the word Waste added before the shipping name.

Samples whose hazards are not yet known, such as a field sample sent for analysis, can be assigned a tentative class, shipping name and packing group based on the shipper's knowledge of the material under 49 CFR 172.101(c)(11), using the most severe reasonable packing group. The word Sample may need to accompany the shipping name. This is not a loophole: the tentative classification must be reasonable.

When a product is not regulated

Many chemicals that are hazardous at work are not hazardous materials in transport. A cleaner that is a mild skin irritant, a paint with a flash point well above 93 °C or a substance toxic only after long-term exposure may be fully covered by OSHA HazCom but not by the HMR. When a material meets no hazard class definition and is not listed, it is not hazmat (unless it is a hazardous substance, hazardous waste or marine pollutant), and shipping it with labels or placards it does not need can mislead responders. The opposite mistake, assuming a product is not regulated because it seems familiar, is more common and more dangerous.