This is a good question. Security of the entire school science department is an important subject that needs to be considered. There is no regulation, as such, written down regarding the locking of science room doors. However, each school should establish and adhere to its own policy. Policies should be developed giving consideration to a risk assessment of the specific site. Science ASSIST strongly recommends that all science rooms are locked, unless a teacher or other authorised person is present.
Laboratories have particular hazards that are not present in ordinary classrooms, such as laboratory glassware, equipment, tools, fire extinguishers and specialist fittings—for example, gas taps. Laboratory benches and equipment may also have residues of chemical or biological materials that present unique hazards. Unsupervised access by students could result in personal injury or damage to property through either accidental breakage or deliberate vandalism.
Science preparation rooms and storage areas have a range of equipment and chemicals that must be kept secure as they have potential for being used for illegal purposes, such as the manufacture of drugs or explosives. An information sheet dedicated to security of the science area is currently being written and will be uploaded soon.
Update: Science ASSIST has developed an ASSIST Information Sheet (AIS) on security in the science area, see AIS: School science area security.