Our comment on proposed USP 800 requirements:
Sentry Air designs and manufactures air purification devices for a variety of industrial and medical applications, including nonsterile pharmaceutical compounding.
We have 30 years of experience in air purification solutions for a variety of workplaces.
We wish to comment on lines 179 and 180 of the latest proposal document.
|179||The C-PECs used for manipulation of nonsterile HDs must be either externally vented|
|180||(preferred) or redundant–HEPA filtered in series|
Power containment hoods, like those used in pharmaceutical compounding, are engineered products.
That means the components – fan, motor, filter depth, interior contours of the hood — are engineered to work together to produce airflow properties that provide measurable protection from unwanted exposure to hazardous particles.
Measurable protection is typically expressed in number of particles in a cubic meter of air.
Generally, a particle count is performed near the operator’s nose and mouth, the breathing zone occupied by the operator as the task is performed.
Changing one component of a product engineered to meet specific objectives actually changes the protective performance of the whole product.
Indeed, the proposal to double up on HEPA filters does exactly that.
(Of course, a product could be engineered to require two HEPA filters to meet a specific objective, but the result would be because of the engineering, not because the product has two filters.)
Filters are not sieves
It’s a common misconception to think of air filters as something like sieves that sift the air; the smaller the ‘holes’ in the filters, the more particles are captured. But that is incorrect.
HEPA filters are effective because of particle physics, not because a specific number of filters are arranged in a series.
HEPA filters capture particles due to the interplay of diffusion, interception, inertia and van der Waals forces, the primary forces that adhere even nano-sized particles to HEPA fibers.
Research has shown HEPA filtration is 99.97% efficient at capturing 0.3 micron particles, the most difficult size to capture. Particles of lesser and greater sizes are captured even more efficiently.
NIOSH says, “When properly sized and installed, HEPA filtration is appropriate for nanomaterial applications both for ventilation systems and respiratory protection.”
Source: NIOSH . Current strategies for engineering controls in nanomaterial production and downstream handling processes. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2014–102.
Sentry Air respectfully requests re-consideration of the proposed two-HEPA filter requirement.
Thank you for your time and consideration.