Nanoparticles are generated as by-products during laser ablation. The size distribution of particlulate emission depends strongly on the applied laser pulse duration. The number frequency of nanoparticles may increase up to 99\% with shorter pulse length. In order to provide safety-related statements on nanoparticles generated during laser materials processing, the particle size distribution during femtosecond laser ablation is studied. The influence of laser parameters, materials, and the process atmosphere on the particle size distribution is examined. Based on data of the production mass rate and particle size distribution, a risk assessment is carried out. Finally, the number concentration, the particle surface area and the mass concentration of nanoparticles in the workplace area are compared with the indicators of toxicological effects available in the literature.