Classification and packing groups

Classification is the first and most important decision in any dangerous goods shipment. It decides the class and division, any subsidiary class, the packing group, the UN number and shipping name, and through them every other requirement: the packaging, the labels and placards, the shipping document, the emergency response assistance plan and the exemptions that may apply. Under Part 2 of the TDG Regulations, the consignor (the person who offers the goods for transport, usually the shipper) is responsible for classifying them correctly. If a consignor cannot classify a product, it must not be shipped until it has been classified.

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 Safety data sheets can be out of date, written for another country, or wrong.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.

Since 2017, the TDG Regulations have required consignors to be able to prove their classification. The consignor must keep a record, such as a test report, a laboratory result, a reference to the product's listing or a classification done with the regulation's criteria, for at least five years, and give a copy to a Transport Canada inspector within 15 days of a request. The rule was strengthened after Lac-Mégantic, where the crude oil's classification was not supported by testing.

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 litre 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 classified provisionally based on what is known about their source, using the most likely class and the most severe reasonable packing group. The TDG Regulations contain specific provisions for samples sent for classification testing. They are not a loophole: the provisional classification must be reasonable and documented.

When a product is not regulated

Many chemicals that are hazardous at work are not dangerous goods in transport. A cleaner that is a mild skin irritant, a paint with a flash point above 60 °C or a substance toxic only after long-term exposure may be fully regulated under WHMIS but not under the TDG Regulations. When a product meets none of the class criteria and is not listed, it is not dangerous goods, 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.