Dangerous Goods

Dangerous goods are articles or substances that could endanger the aircraft or the people in it if they leaked, reacted, caught fire or exploded in flight. The United States calls them hazardous materials, or hazmat. Fuel in a can, a cylinder of compressed gas, a car battery, a pot of paint and a spare laptop battery are all dangerous goods, and so are less obvious items such as dry ice and magnetised equipment.

Most of them travel safely by air every day. What makes that possible is a single chain of rules: the shipper classifies, packs and labels the goods, the operator checks and accepts them, the loaders stow them where they belong, and the commander is told in writing what is on board and where. A break anywhere in that chain has caused fatal accidents, which is why dangerous goods are part of every pilot's theory syllabus and every airline's recurrent training.

What are dangerous goods

ICAO Annex 18 contains the Standards and Recommended Practices, and its Technical Instructions for the Safe Transport of Dangerous Goods by Air (Doc 9284) hold the detail: the list of dangerous goods, packing, labelling, documentation, training, and what may travel in the cabin or on the flight deck. The exam definition describes dangerous goods as articles or substances capable of posing a significant risk to health, safety or property when transported by air. The airline industry works from the IATA Dangerous Goods Regulations, which are based on the Technical Instructions.

In Europe, an operator needs a specific approval under Part-SPA, Subpart G to transport dangerous goods. The rules are not limited to commercial flying: under Part-NCO a private pilot may not carry a can of spare petrol in the baggage compartment either. In the United States the Hazardous Materials Regulations, 49 CFR Parts 171 to 180, apply to every operator whatever part of 14 CFR it flies under.

Two groups of items are excepted from the full provisions. The first is what the aeroplane needs to operate: the fuel in its own tanks, its installed batteries, its fire extinguishers and oxygen, and the items provided for catering and passenger service. The exception rests on the function the item serves, not on its being harmless, so an item carried as a replacement, such as a spare medical oxygen bottle for a patient, is dangerous goods and travels under the Technical Instructions. The second group is the limited range of items that passengers and crew may carry under Part 8 of the Technical Instructions.

Hazard classes and divisions

Every dangerous substance is assigned to one of nine hazard classes, several of them split into divisions. The order is fixed and worth knowing by heart, because a NOTOC gives the class number and nothing else to explain it.

The divisions matter to the crew. Division 4.3 substances release flammable gas on contact with water, so water is the wrong first agent on a damaged 4.3 package. The infectious substance label carries the instruction to notify the public health authority at once if the package is damaged or leaking.

UN numbers, shipping names and packing groups

A UN number is a four-digit number assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods to a single substance or a group of substances. It is always used with the proper shipping name, the standard name of the entry in the list, so that anyone from the shipper to a fire officer can look up the same entry and its emergency response.

Within a class, substances are ranked by a packing group: I for high danger, II for medium and III for low. The packing group sets how strong the packaging must be and how much may go in one package. It says nothing about which type of aircraft may carry the package; that is decided by the quantity limits for passenger and cargo aircraft.

View full schematic

Labels and Cargo Aircraft Only items

Each package carries its UN number and shipping name and a hazard label for its class or division, coloured and with the class symbol, as in the table above. Handling labels add information that is not a hazard class. Two are examined often:

• Cargo Aircraft Only (CAO): black on orange, 120 mm by 110 mm. The package may travel only on a freighter, because the permitted quantity is larger than is accepted on an aeroplane carrying passengers. It must never be loaded on a passenger flight, whatever the circumstances.
• Magnetised material: blue on white, 110 mm by 90 mm. The contents produce a magnetic field strong enough to disturb the aircraft's compasses, so the package is stowed with that in mind.

Transport document and acceptance checklist

Responsibility is split. The shipper must offer the goods correctly classified, packed, marked, labelled and documented. The operator remains responsible for their being carried, packed and labelled as the Technical Instructions require, and it checks rather than trusts.

An operator may not accept dangerous goods unless they come with two copies of the dangerous goods transport document, the shipper's declaration, except where the Technical Instructions say otherwise. Acceptance staff then work through a dangerous goods acceptance checklist, item by item, to confirm that the document, markings, labels and packaging of each consignment comply. Packages are inspected for leakage and damage before loading, and a leaking or damaged package is not loaded. Dangerous goods are kept out of the passenger cabin and the flight deck unless the Technical Instructions specifically allow them there, and packages whose contents could react with each other are segregated in the hold (see cargo loading and floor limits).

The NOTOC

When dangerous goods are carried, the operator must give the commander written information about them before departure, commonly called the NOTOC (notification to captain). For each consignment it gives the proper shipping name, the class or division, the UN number, the quantity and the loading position. Under 49 CFR 175.33 the US version also confirms that no damaged or leaking packages were loaded; the pilot in command keeps it readily available in flight, and a copy stays on the ground.

Commercial details have no place on it, because the NOTOC exists for one moment: an emergency. If one occurs in flight, the commander informs the appropriate air traffic services unit, as soon as the situation permits, of the dangerous goods on board, so that the rescue and fire-fighting services know what they will face and exactly where it is stowed before the aircraft lands.

Will-carry and will-not-carry operators

In the United States, a Part 121 carrier's operations specifications state whether it is a will-carry or a will-not-carry operator. A will-carry operator accepts hazardous materials as cargo and complies with the full 49 CFR requirements for acceptance, packaging, labelling, loading and notification. A will-not-carry operator does not accept them, and trains its staff to recognise hazardous materials so that they can be refused, because undeclared items in cargo and baggage are a leading cause of cargo fires. Under Part 121 Subpart Z every carrier needs an approved hazardous materials training programme, whichever it is. The European equivalent of the distinction is simply whether the operator holds the Part-SPA approval.

Passengers, crew and lithium batteries

What passengers may carry is set out in Part 8 of the Technical Instructions and in the airline's own rules, which may be stricter. Lithium batteries, both lithium-ion and lithium metal, are Class 9 dangerous goods, and the carriage rules for passengers turn on the battery's rating in watt-hours, which is usually printed on it.

Spare batteries, including power banks, go in the cabin only, with the terminals protected against short circuit, because a battery fire must be seen and fought at once and that is impossible in a hold. Batteries installed in a device may travel in the cabin or in checked baggage; the US rules add that a device in checked baggage must be switched off and protected from accidental activation. As cargo, lithium batteries are packed and declared under the Technical Instructions like any other dangerous goods. A lithium battery fire can exceed the capability of a cargo hold's fire suppression system, one reason these shipments receive so much regulatory attention.

Dry ice, magnetised material and mercury

Dry ice is solid carbon dioxide used to keep perishables and medical shipments cold. It sublimates into carbon dioxide gas, which displaces oxygen in a confined cabin or hold, so the packaging must let the gas vent. A passenger may carry up to 2.5 kg, with the operator's approval; the limit applies per person, not per package.

Magnetised material is a hazard to navigation rather than to people: a strong enough field deflects the compasses and the heading reference. The blue-on-white label warns the loaders to keep it away from them.

Mercury is the aviation example of a corrosive spill. Carried in instruments such as barometers, it attacks aluminium alloys by amalgamation, penetrating the grain of the alloy and destroying it in a very short time. It runs through small cracks to the lowest points of the structure. A mercury spillage must therefore be reported and cleaned up at once: the mercury is collected, typically by vacuum, and never blown about with compressed air, which scatters it, and the structure is then inspected.

Dangerous goods incidents and accidents

Dangerous goods incidents and accidents, from a leaking package to a fire on board, must be reported to the authority, with the first report despatched within 72 hours of the event unless exceptional circumstances prevent it. In this context a serious injury includes hospitalisation for more than 48 hours beginning within seven days of the injury.

The loss of ValuJet Flight 592 in 1996 shows why the chain matters. Chemical oxygen generators were carried in the cargo hold without being declared or packed as dangerous goods. Once activated, such a generator cannot be stopped and its surface can reach 232°C, and the fire that followed brought the aircraft down. Undeclared dangerous goods remain one of the main causes of cargo fires, and in flight the crew's defence is the procedure described in in-flight fire, smoke and fumes.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.