Working at Height
Bit late to the party but I thought I'd throw my 2 cents in anyway.
The intent behind the rules and regulations around working at height is to prevent a person from falling a distance which will cause significant injury or death.
Looking at what guidance there is for what is deemed a height where, if you were to fall, is likely to cause significant injury or death is 1000mm (based on the building code).
At any height greater than 1000mm, some form of controls are required. Based on the hierarchy of controls, Eliminate is generally impossible, substituting is likely difficult to achieve, engineered controls like fixed barriers are the most common control, then it turns to PPE and administrative controls (harnesses, scaffolding, mobile work platform, PTW, JSEA,etc)
While it is a broad coverall statement, if the level is greater than 1000mm, a means to prevent falling is required.