Exposure to Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 342

tend not to take account of agglomerated particles. However, it is not easy to be
confi dent that in all workplaces where these materials are being manufactured or
used, an adequate assessment of the risks has or will be made. Nevertheless, assess-
ment of risks has to be made on the best available information and control strate-
gies will have to be developed based on these assessments.
Strategies to control exposure to nanoparticles may include:

• Total enclosure of the process
• Partial enclosure with local exhaust ventilation
• Local exhaust ventilation
• General ventilation
• Limitation of numbers of workers and exclusion of others
• Reduction in periods of exposure
• Regular cleaning of wall and other surfaces
• Use of suitable PPE
• Prohibition of eating and drinking in contaminated areas.

Choices for each of these will need to be made based on some understanding of
the differences between nanoparticles and larger particles.

8.4.2 Inhalation Exposure

8.4.2.1 Engineering Control

For air velocities prevailing in workplaces, airborne nanoparticles can be consid-
ered as having no inertia. They will, therefore, behave in a similar way to a gas and
if not fully enclosed, will diffuse rapidly and will remain airborne for a long time.
Because of their high diffusion velocity, these particles will readily fi nd leakage
paths in systems in which the containment is not complete. Engineering control
systems designed for use to control nanoparticles, such as enclosures, local ventila-
tion or general ventilation, therefore need to be of similar quality and specifi cation
to that which is normally used for gases rather than for particulate challenges. These
systems do exist and are in common use in the chemicals and other industries. Like
all such systems, however, effective performance is highly dependent on appropri-
ate use and maintenance.
No relevant research has been identifi ed that has specifi cally sought to evaluate
the effectiveness of engineering control systems against new nanoparticle chal-
lenges. While most of these systems can in principle be used to control exposure,
they do not always do so. There is no reason to expect that application of these
methods to new nanoparticle generation processes will result in better control than
that previously demonstrated in micro-scale powders and in gases.

8.4.2.2 Filtration

Filtration plays an important role in the control of exposure to airborne particles.
High Effi ciency Particulate Arrester (HEPA) fi lters are used in engineering control
systems to clean the air before returning it to the workplace. These fi lters are usually
referred to as mechanical fi lters.