Many types of materials ranging from biological hazards to nuclear waste are shipped across the nation daily. Though each cargo has the capacity to do serious harm, a large number of regulations exist so that the threat is kept to an absolute minimum. Shipping dangerous goods under the auspices of the United States Department of Transportation keeps all hazmat transports regulated by federal code, dictating that the contents must be sealed and marked individually so as to provide the smallest element of risk to handler and shipper. This is done under the umbrella of seven separate classes of goods.
Explosives, the first class of dangerous goods, can be anything from TNT used for mining operations to ammunition and highly flammable goods. They must be marked according to their ability to cause damage, ranging from minor blast hazards like fireworks to extremely fire-sensitive materials like rocket fuel.
The second class are gases, substances that may be corrosive, poisonous, or flammable. Poisonous gases like chlorine are the easiest to transport, given that nothings short of extremely high pressure will puncture the hull. Flammable gases, conversely, are some of the most dangerous as they can be set alight with a single spark.
Flammable liquids are a separate entity given their capacity for boiling at certain temperatures. Simple gasoline can withstand temperatures of up to one hundred fifty degrees, while carbon sulfide must be kept at a much lower temperature.
Flammable solids are much rarer than liquids, as they are rarely used for fuel. Some solids, like calcium, may react violently with water and must be kept away from moisture at all costs. Others can ignite spontaneously like white phosphorus; still others like spent nuclear fuel can catch fire without producing flame.
Organic peroxides like potassium permanganate and ammonium nitrate are capable of quickly killing any material they come in contact with and must be kept sterile at all times.
Any infectious substances, such as virus specimens or used needles, must be shipping according to World Health Organization standards rather than American regulations, given that any potential spread of the infection could affect other nations.
Radioactive substances, usually uranium or plutonium, will emit radiation during their transport and must be sealed in lead, then transferred immediately to a safe storage location.
Corrosive materials that can quickly erode metal or human tissue, like hydrochloric acid, are relatively safer to transport given that they can be exposed to air.