According to Australian Forklift Training it is illegal for a forklift operator to drive with a passenger sitting or standing on some part of the forklift, which should not be allowed.
Standard forklifts are only designed to carry one operator at a time. Their safety guards and seating only protect the person sitting in the seat. They are also stability tested only to handle the weight of one operator, who is sitting in the operating position.
When a passenger is injured, all sorts of problems can arise. Minor injuries can bring unnecessary workers compensation claims and a visit from WorkCover to discuss why this happened and how the company is going to fix it. If the passenger is seriously injured or killed, the individual operator can be charged and the company will get a major investigation from WorkCover, followed by a fine and further follow up investigation.
It is important to take a strong stance against operators carrying passengers on a forklift. Those who are seen carrying passengers need to be reprimanded immediately as the consequences of letting them to continue can be disastrous.
There are forklifts on the market which are specially designed to carry two people. The practical advantages of being able to carry two people however are very limited. Some Navy and mining sites use them for training purposes or when they need to take a spotter to a job with them.
Most companies have no real need to carry a passenger, so Australian Forklift Training recommend that companies enforce a strict no passenger policy to avoid unnecessary problems.