n 30 SEPTEMBER 2015 | PHARMACEUTICAL PROCESSING
nPHARMPRO.COM n DUST EXPLOSIONS
Explosion hazards associated with powders will influence the specification of operating procedures, process equipment, HVAC systems, electrical area classification and room construction. It is therefore
necessary for OSD manufacturers to clearly understand the
deflagration hazards presented by the powders utilized in
their processes and be able to assess the level of deflagration
risk that their operations may present.
Deflagration is a term describing subsonic combustion
propagating through heat transfer (i.e., hot burning material
heating the next layer of cold material and igniting it).
It is the expectation of the Occupational Safety and Health
Administration (OSHA) that employers maintain a workplace
free of hazards that are likely to cause injury or death to employees, including combustible dust deflagration hazards.
In addition, OSHA
expects employers to assess dust explosion hazards and apply appropriate safeguards in keeping
with current codes,
standards and best practices to prevent injuries.
One new standard that
is applicable to all pow-
is NFPA 652 - Standard
on Fundamentals of Combustible Dusts, 2016 Edition (Ref. 1)
which states that the facility, processes and equipment shall
be designed, constructed, equipped and maintained. And
management systems shall be implemented to:
1. Reasonably protect occupants not in the immediate proximity of the ignition from the effects of fire for the time
needed to evacuate, relocate or take refuge.
2. Prevent serious injury from flash fires and explosions.
3. Ensure the ongoing production/operating capability of the
DUST CLOUD DEFLAGRATION HAZARDS
When finely divided combustible powder particles are
suspended in air in sufficient concentration and ignited by a
sufficiently energetic ignition source, a combustion reaction
can propagate through the dust
cloud. If the speed of the flame-
front through the unreacted
medium is less than the speed
of sound, the event is, by defini-
tion, a deflagration.
These rapid combustion
processes create extreme temperatures (and possibly combustion gases) which cause a
pressure wave to precede the
flame-front. The pressure wave
moves through the unburned
dust cloud at the speed of
sound. This pressure wave and
Dust Deflagration Hazards in
Pharmaceutical OSD Facilities
and the Requirements of the
New NFPA 652
Many of the powders that are used in the production of pharmaceutical oral
solid dosage (OSD) formulations are combustible, and since most operations in
pharmaceutical facilities can create explosible atmospheres, dust cloud explo-
sion hazards should be expected.
n By Vahid Ebadat, Ph.D., Chilworth Technology, a DEKRA Insight Company