Form 16 is the Queensland Development Code form used for compliance certification on building work. The form is signed by an RPEQ engineer (Registered Professional Engineer of Queensland) certifying that a particular aspect of a project (design, inspection, construction) complies with the relevant standards.
For steel gates, fences, and balustrades in Queensland, a Form 16 is required when the local council or private certifier asks for engineering certification on the structural design or installation. Pool barriers, public-access balustrades, and any commercial gate over a threshold size all typically attract a Form 16 requirement.
Other Australian states use different forms but the principle is the same: a registered engineer signs off that the work complies with AS standards and the NCC.