In Victoria, under a mandated industry standard, double adaptors cannot be used on building sites.
There is no legislation which prevents the use of double adaptors in other other workplaces. The Office of the Chief Electrical Inspector advises using these with extreme caution, however. They should never be "piggy-backed", for example, and care should be taken that use of double adaptors does not create other hazards, such as tripping hazards.
The Officer of the Chief Electrical Inspector (now Energy Safe Victoria) has produced guidelines on
- Switches, leads and powerpoints
- The Safe Use of Power Boards (pdf)