Nerve agents and substances causing injury to the skin and tissue are easily soluble in, and penetrate many different types of material, which renders decontamination more difficult. If chemical warfare (CW) agents have penetrated sufficiently deep, then toxic gases can be released from the material for long periods.
To be a jockey, there are no height limits, only weight limits. A rider can be of any height if they can still make weight, but it is still generally limited to fairly short individuals because of the limits on a person's body. Jockeys typically range from 5' to 5'7 in height. No need to lose any weight.
So if you just go by height, a pony becomes a horse when it grows past 14.1... a horse becomes a pony when it fails to make that 14.2 cut off. If you go by people's opinions, the pony is in the eye of the beholder, and if you go by breeds, it's whatever the breed standard says, and if you go by shows, you follow the particular rules.