A.
In 1953, United Nations voiced the need for a regulation that will help maintain safety in the transport of dangerous goods. A few international airlines responded, and after 3 years of concentrated work, the IATA Restricted Articles Regulations First Edition was published in 1956. At that time when designing the 3-letter codes, the letter “R” was brought from the word “Restricted” and placed as a first letter of the 3-letter code. The balance 2 letters were to be the acronym of the substance, such as RFL for Flammable Liquid. Since then Restricted Articles Regulations have been changed to Dangerous Goods Regulations however the letter “R” was not changed to letter “D” as it was too costly in the computer age to change, and was left untouched.

As for the code “RPB” for toxic substances, toxic substances were called “poison” in those days therefore the letter “P” for the second letter. In those days there were 3 classes of poison and were consequently coded as RPA, RPB and RPC. Later RPA was raised to Toxic Gas and became RPG. RPC was downgraded and became “not restricted”. Thus “RPB” only remained and is being used to date. If letter “P” for Poison is to be changed to letter “T” for Toxic, it will again be costly so it is placed as status quo.