Biomedical Engineering Reference
In-Depth Information
face (ACGIH, 2010). Higher ventilation rates are selected for hoods with poor air distributions, such
as disturbance from traffic past hoods, or nearby ceiling-grille/diffuser-supplied air. Studies have
shown that the escape of nanomaterials from chemical hoods can occur when the hood face veloc-
ity is below 80 feet per minute (fpm) or above 120 fpm (Tsai et al., 2009). A low velocity allows
the supposedly exhaust air to exit the hood, whereas a high velocity causes a strong turbulent wake
in between the worker and the hood face, both of which can carry or pull nanomaterials out of the
hood. Conventional, constant-flow hoods, in particular, are prone to such problems if the sash is not
positioned at a proper height. Better alternatives include the by-pass hood and the constant-velocity
hood. Recently, a novel air-curtain chemical hood was developed under the support of the Taiwan
Institute of Occupational Safety and Health (IOSH) (Huang et al., 2007) and shown to be effective
in containing airborne nanoparticles inside the hood due to the downward air-curtain from the
double-layer sash (Tsai et al., 2010). Finally, owing to the unknown hazards from nanoparticles, the
exhaust air of the LEV should be filtered or scrubbed, whenever feasible, before venting outdoors
and should not be recirculated indoors.
In addition to chemical hoods, glove boxes, BSCs, and powder handling enclosures could be
effective at containing airborne nanomaterials when appropriate practices and operations are
followed. A glove box enclosure provides a better means for isolation between the workers and
nanomaterials and, hence, better protection. However, extra cautious steps must be given when
transferring nanomaterials into, out of, and when cleaning the glove box. BSCs are designed spe-
cifically for the handling of microorganisms (e.g., virus and bacteria), which are in a range of sizes
similar to nanomaterials. With a sophisticated HEPA-filtered airflow design, the most widely used
and readily available Class II BSCs provide protection to not only the worker but also to the product
and the environment. However, the complex airflow patterns inside the cabinet may cause the loss of
nanomaterials. Powder handling enclosures are typically small, ventilated enclosures for handling
small quantities of dry powders. Unlike chemical hoods, the relatively low airflow rate and veloc-
ity in the powder handling enclosure reduces the potential for the loss or escape of nanomaterials.
2.5.2 a
dMINIstratIve
c
oNtrols
Administrative controls are a critical and integral part of control strategies, as they are crucial to the
awareness, practices, and procedures adopted by workers to minimize exposure and complement
engineering controls. On the other hand, a designated work area should be given to nanomaterial-
related operations and processes. The designated area can be a laboratory, a specific area, or an
enclosure with its entry posted with signs of potential hazards, PPE requirements, and access only
to authorized personnel. To avoid the migration of nanomaterials outside the designated area, the
use of walk-off pads, the creation of a buffer zone, and the installation of decontamination facilities
are advisable. In addition, the number of nanomaterial workers and the duration of work should be
reduced as much as is practical.
2.5.2.1 Employee Training
Employee training is arguably the most important element of administrative controls. It aims to
communicate and educate workers, as well as their employers, on the presence of potential hazards,
safe work procedures, good personal hygiene, regular housekeeping, the proper disposal of nano-
materials, and the use of PPE. Among them, hazard communication is the foundation of successful
administrative controls, because both the workers and employers need to know exactly why precau-
tious practices are required for working with nanomaterials, such that they are fully involved in the
nanomaterial-related safety and health issues. Furthermore, the workers need to know the proce-
dures to perform their work (e.g., transfer, label, storage, cleaning, and disposal) efficiently and in
a way that minimizes exposure. As nanomaterial health and safety sciences are evolving rapidly,
there is a need to regularly update training programs when new information is available.
