Filter options and comparisons
6.1.8.5 Avoiding problems with HEPA filter performance:
5081 5082
There are some specific issues with HEPA filters that have been 5083
observed in recent years in pharmaceutical cleanrooms which require 5084
some attention to detail in order to avoid. Two of these are 5085
5086
HEPA filter gel seal degradation, and 5087
HEPA filter bleedthrough.
5088 5089
HEPA filter gel seal degradation- 5090
5091
Degradation of gel seals has been observed in cleanroom applications as 5092
silicone (siloxane) gel which appears to revert to a liquid state and 5093
begins dripping out of the gel track. This is sometimes accompanied by 5094
a color change, such as fading to a clear or translucent appearance.
5095
This most often does not result in an observed integrity failure of the 5096
Crosslinking of the gel components 5103
5104
The more complete the crosslinking, the less unbonded polymer 5105
to migrate to the surface 5106
The specific gel type and the mixing (ratio of components, 5107
environmental conditions, time to complete the reaction, etc.) 5108
are key to amount of crosslinking.
5109 5110
Molecular weight of the gel 5111
5112
Higher molecular weight reduces the diffusion and migration of 5113
unbonded polymer diffusion 5119
5120
Acts as a solvent, increasing migration of unbonded polymers 5121
to the surface 5122
It does not appear that typical pharma cleanroom cleaning and 5123
sanitizing agents (such as bleach, hydrogen peroxide, etc.) 5124
affect the rate of unbonded polymer diffusion.
5125 5126
It is also recommended that miter joints and penetrations of the filter 5127
gel track be sealed with a material proven to be impervious to the 5128
silicone gel components (i.e., silicone gel components will penetrate 5129
silicone caulk). Urethane gels are not recommended as replacements for 5130
silicone gels in pharma cleanroom applications that will be exposed to 5131
cleaning and sanitizing chemicals, since their performance is affected 5132
by those chemicals as well as being affected by aerosol challenge 5133
materials such as PAO and DOP.* The filter manufacturer can help 5134
determine the appropriate silicon gel that maximizes crosslinking and 5135
molecular weight and provides satisfactory sealing characteristics 5136
(resiliency, adhesion, etc.). Reducing the amount of aerosol challenge 5137
also form a tough skin on its upstream side, leading to poor bonding at 5143
the gel/knife edge interface. Fading of color does not appear to affect 5144
ability of the gel to cure.
5148
5149
HEPA filter bleedthrough 5150
filters and to applications in which thermo-pneumatic (hot-block) 5159
aerosol generators were used for testing. Studies into the nature of 5160
this problem have resulted in determining that the following factors 5161
are crucial to understanding and avoiding the bleed-through problem:
5162
- Impact of velocity on filter efficiency and bleed-through.
5167 5168
- Methods for specifying and testing HEPA filters 5169
5170
Particle size distribution of the challenge aerosol from the generator- 5171
5172
Aerosol particle sizes generated from Laskin-nozzle type generators are 5173
stating the efficiency of the filter at the filter's MPPS.
5184 5185
Impact of velocity on filter efficiency and bleed-through- 5186
5187
Air velocity has a significant impact on filter performance. Increasing 5188
should be specified for the intended face velocity.
5193 5194
Methods for specifying and testing HEPA filters- 5195
5196
Bleed-through problems have been noted in filters that are integrity 5197
tested with hot-block generated aerosols up through commercially 5198
their factory test conditions. This may occur when:
5204 5205
- Actual field velocities are higher than factory tests 5206
Recommended practices to avoid the bleed-through problem would be to:
5214 5215
- Specify the filter for the velocity it will see in the installation 5216
an IEST Type K or an EN-1822 Type H14 with a local penetration limit of 5223
two times the global penetration (i.e. 0.01%) instead of the standard 5224
five times (0.025%) as called for in EN-1822.
5225
Metal and Air Conditioning Contractors‘ National Association (SMACNA) 5230
and Heating and Ventilating Contractor‘s Association (HVCA) standards.
5231
Ductwork should be constructed of galvanized sheet metal. Stainless 5232
steel should be used when corrosion and continual cleaning occur. There 5233
support and connections should be considered. When flexible ductwork is 5238
avoided otherwise increased noise, vibration, and pressure drop will 5243
result. Provide sufficiently sized duct access doors at appropriate 5244
locations to equipment (e.g. coils, humidifiers, control boxes, 5245
dampers). To preclude air leakage all ductwork shall be sealed with 5246
approved fire and smoke rated sealant in accordance with NFPA 255 or UL 5247
723 or equivalent. Ductwork leak testing percentages will vary from 5248
site-to-site, air system, and areas served. Recommendations include 5249
the following performances for various applications. Ductwork should 5250
have 1% leakage with 0% leakage on positive pressure exhaust, 4‖ w.g 5251
(0.996 kPa) minimum static pressure class, and a maximum seal class A.
5252 5253
6.1.10 Dampers and Louvers 5254
5255
Dampers are used to redirect, stop and vary the amount of air traveling 5256
within an HVAC System. Damper blade movement can be either parallel or 5257
opposed. Parallel blade dampers rotate in the same direction so that 5258
they stay parallel to each other throughout their travel from full open 5259
to full closed. Opposed blade dampers operate such that adjacent 5260
blades rotate in the opposite direction from each other.
5261 5262
Opposed blade dampers are preferred for their smooth throttling flow 5263
for they have a more linear performance due to less turbulence.
5264
streams into each other.
5270
snow, openings shall be equipped with a 90-degree gooseneck inlet sized 5276
for a maximum of 1.02 m/s (200 FPM) and shall be equipped with an inlet 5277
louver sized for the same velocities. All louvers shall be drainable 5278
and be constructed of anodized aluminum or stainless steel with 304 SS 5279
hardware, and include 304 SS bird screens.
5280 5281
Wind driven rain can be forced into outside air intakes with such force 5282
the rain can be pulled thru the air handling sections and sent down the 5283
supply ductwork. It is advisable to select a storm louver for outside 5284
air intakes that meet those rare occasions for unseasonable weather to 5285
avoided pulling moisture into system.
5286
mechanically attached (not glued) to the damper blade and jamb seals to 5292
prevent leakage around the ends of the damper blades.
5293
be made of corrosion-resistant materials of aluminum or 304 SS. Damper 5297
jackshaft should be extended to the exterior of the AHU for actuator 5298
mounting for interior AHUs.
5299
pipe and cooling towers, which can have a negative effect on indoor air 5303
quality. There are local and regional codes that provide minimum 5304
distances and these requirements must be followed.
5305 5306
6.1.11 Diffusers and Registers 5307
5308
These devices are critical to the air distribution in and out of 5309
spaces. Proper positioning is vital for providing good distribution and 5310
a sweeping action of the air from the supply to the return side of the 5311
space to deliver uniform air patterns to cleanse the environment and 5312
displace contaminants. Poor positioning can result in either dead 5313
zones, which can cause an increase in particulates levels, or excessive 5314
airflow, which can cause unwanted air turbulence.
5315 5316
Since these devices are located at the perimeter of the space (ceilings 5317
and walls), the choice of materials must be evaluated for compatibility 5318
aggressive cleaning agents.
5322
the room. Refer to the Filtration section for more detail.
5326 5327
6.1.12 Ultraviolet (UV) Light 5328
5329
Ultraviolet light is an engineering control that may be used to 5330
supplement the existing filtration device(s) in a building‘s HVAC 5331
caused by fouling.
5335 5336
UV light has a wavelength of 100 – 400 nm, with the UVC (200 – 280 nm) 5337
wavelength considered the germicidal killing range, since it 5338
effectively inactivates bacteria and viruses. When microbes (bacteria, 5339
bacterial spores, viruses, yeast, mold and mold spores) are exposed to 5340
sufficient doses of UVC light, their DNA is destroyed, causing cell 5341
death or making replication (cell division) impossible. The optimal 5342
microbial inactivation when exposed to the UV radiation. However, it is 5348
intensity/dosage needed to inactivate the microorganisms you are 5354
looking to control.
5355 5356
Ultraviolet germicidal irradiation (UVGI) systems are typically 5357
comprised of a series of lamps and ballasts. The recommended 5358
construction should include stainless steel lamp holding assembly and a 5359
economic means of boosting the average intensity field without 5363
additional power consumption. The system shall be safeguarded against 5364
accidental UV exposure. Air temperature is a consideration when 5365
specifying a cooling coil irradiation UV system, as the temperature 5366
inside the lamp is directly related to the UV output obtained.
5367 5368
Since accumulation of dirt will decrease both the effect and life of 5369
the UV lamps, high efficiency upstream filtration is needed.
5370 5371
6.1.13 Reliability and Maintenance Enhancements 5372
5373
The reliability and maintenance of equipment is of utmost importance 5374
within the pharmaceutical industry. Robust design and construction of 5375
HVAC equipment will increase their reliability and maintainability to 5376
perform properly from the start up of the operation and will continue 5377
beyond their normal anticipated life when they are properly maintained.
5378
Good maintenance procedures performed in a timely manner will over the 5379
life of the equipment, reduce costs and will have a positive impact on 5380
the outcome of the production process. Vivariums are extremely 5381
sensitive operations with long-term studies that require reliable and 5382
redundant systems, so as to achieve steady environmental conditions.
5383 5384
The following are some of the reliability and maintenance items that 5385
should be included:
5386
Vibration monitoring of blower and motor bearings 5390
Automated lubrication 5391
Bearing life of ABMA L10 200,000 hours 5392
Lower rotation speeds of motors and fan wheels 5393
High efficiency filters 5394
5395
6.1.14 Energy Reduction 5396
be designed to reduce airflow during unoccupied periods for all or part 5401
of the system.
5402 5403
Designers are urged to fully investigate the required internal design 5404
criteria to avoid unnecessary energy use, to meet excessive high or low 5405
temperature or humidity requirements. This is also relevant for values 5406
of air change rates and pressure differentials. Similarly the external 5407
design conditions should also be investigated, to avoid over sizing of 5408
systems resulting in less than optimal performance and added project 5409
and operational costs.
5410 5411
Dedicated units for areas with specific requirements (i.e., longer 5412
hours of operation, lower or higher temperature and humidity, specific 5413
processing equipment, etc.) should be specified that would allow for 5414
the shut down or set back of central systems.
5415 5416
The control and use of outside air should be carefully evaluated to 5417
avoid additional air quality conditioning, resulting in a substantial 5418
energy penalty. The guidelines established in ASHRAE 62.1, Ventilation 5419
for Acceptable Indoor Air Quality, should be followed to ensure a 5420
healthy indoor environment.
5421 5422
Designers are urged to increase air handling coil area, distribution
costs should be significantly greater than that, which would occur from 5426
the increased capital costs over the life of the building.
5427 5428
Avoid over sizing equipment for future needs unless it is deemed a 5429
likely probability to occur, as this could mean that a fan or pump will 5430
be operating at an inefficient part load condition. If this is 5431
unavoidable, use VFD control of the fan or pump.
5432 5433
6.1.14.1 Air Filtration Systems