A relevant first-aider who has a current certificate in the use of nitrous oxide (S4) granted by a registered training organisation may (a) possess nitrous oxide (S4); and(b) administer it, or supply it for self-administration, to a person, on the oral instruction of a medical practitioner; and(c) administer it, or supply it for self-administration, to a person, on the written instruction, other than on a standing order, of a medical practitioner; and(d) in an emergency, administer it, or supply it for self-administration, to a person, without instruction from a medical practitioner.