The Working Conditions Act obliges employers and clients to ensure a safe and healthy working environment. This duty of care also applies to freelancers working on-site for a client (Articles 3 and 16 of the Arbowet). In practice, this means the client is responsible for the physical working conditions at the workplace, even when you're working there as a freelancer.
For psychosocial safety at work, such as protection against harassment, bullying, or sexual harassment, the situation is different. The Arbowet obliges employers to pursue policy to prevent psychosocial workload (Article 3, paragraph 2 of the Arbowet). But this obligation applies to employees. That means people working under an employment contract, but also people who don't have an employment contract but do factually work under the client's authority. As a freelancer who works independently and on equal footing with a client, you generally don't fall under that protection. However, if you do in fact work under your client's authority, you can be classified as an employee within the meaning of the Arbowet, meaning the client also has the psychosocial workload obligation from Article 3 paragraph 2 towards you. This therefore depends on the actual nature of the collaboration, not the contract form. More on this under the section on disguised employment (schijnzelfstandigheid). This doesn't mean that, if you don't work under authority, you have no options at all if you experience unwanted behavior at work. But the route then doesn't run through the Arbowet, but through the civil courts or through contractual agreements with the client.
Nevertheless, the policy around psychosocial safety within the organization where you work as a freelancer, such as a formal complaints procedure, may have been extended to freelancers. In that case, those procedures and the confidential counselor could also be open to freelancers. More on this shortly.
As a freelancer, you also have your own legal obligation under the Arbowet: you're required to take care, to the best of your ability, of your own safety and health and that of others at the workplace. This obligation concerns practical and physical aspects of safe working, such as properly using work equipment and protective equipment, and reporting hazards. The law doesn't impose an obligation on freelancers specifically regarding social safety or preventing unwanted behavior: the provision on psychosocial workload (Article 3, paragraph 2 of the Arbowet) is not included in the limited list of articles that apply to the self-employed.