HEPA filter | Sterile Manufacturing Unit | HEPA filter classification | HVAC System

HEPA filter | Sterile Manufacturing Unit | HEPA filter classification | HVAC System

In the pharma industry, HEPA filters are a prerequisite for foreign particle controls. External particles are considered to be a source of contamination. Hence, viable and non-viable particle count monitoring is a prerequisite in the pharma industry, especially in sterile formulation plants. To implement these controls HVAC system is designed.

Introduction to HEPA Filter and HVAC System:

For sterile formulation, the HVAC system is a major utility for controlling the production area. For sterile formulation units, class gradation is required to be maintained as the production areas in sterile manufacturing areas are more critical. It is a very big challenge to the engineering team to maintain the HVAC system in the grade A area. Hence proper selection of HEPA filter as per HVAC system is more important.

Which size of the filter is used as a terminal filter in AHU - HEPA filter classification?

For maintaining aseptic areas, a 0.3 µ terminal filter is used. (90% down to 0.3 µ). The type of filter rating which provides 0.3 µ is EU-13, EU-14. The typical filter rating is provided in the below table.

Sr. No.	STD EC Grade	Occupancy Condition	Particles / M3		ISO Classification	Particles / M3
			≥ 5 µ	≤ 0.5 µ		≥ 5 µ	≤ 0.5 µ
1	Grade A	At Rest	20	3,520	ISO Class 5	29	3,520
		In operation	20	3,520
2	Grade B	At Rest	29	3,520	ISO Class 7	2,930	3,52,000
		In operation	2,900	3,52,000
3	Grade C	At Rest	2,900	3,52,000	ISO Class 8	29,300	35,20,000
		In operation	29,000	35,20,000
4	Grade  D	At Rest	29,000	35,20,000	ISO Class 9	2,93,000	35,20,000
		In operation	Not Defined

Selected ISO 209 airborne particulate cleanliness classes for clean rooms and clean zones.

numbers (N)	Maximum concentration limits (particles/m^3 of air) for particles equal to and larger than the considered sizes shown below
	0.1 µ	0.2 µ	0.3 µ	0.5 µ	1 µ	5.0 µ
ISO 1	10	2
ISO 2	100	24	10	4
ISO 3	1 000	237	102	35	8
ISO 4	10 000	2 370	1 020	352	83
ISO 5	100 000	23 700	10 200	3 520	832	29
ISO 6	1 000 000	237 000	102 000	35 200	8 320	293
ISO 7				352 000	83 200	2 930
ISO 8				3 520 000	832 000	29 300
ISO 9				35 200 000	8 320 000	293 000

What are the particle sizes monitored during non-viable particle count?

Daily and during batch processing non-viable particle count is being monitored. For monitoring, only 0.5 µ and 5 µ particle size are being monitored. For grade, A 1000 Liters of air must be sampled for the non-viable count. These particle counts are measured by portable particle counter and online particle count measuring devices. Below are examples of particle monitoring devices.

Why only 0.5 µ and 5 µ particle sizes are being monitored for aseptically controlled areas?

Typically, HEPA filers are of 0.3µ size. Hence, only particles that are smaller than 0.3 µ will come through the HEPA filter. But due to man material movement, particles bigger than 0.3 µ  will contaminate the area. 

Most bacteria come under the size range of 0.5 µ and 5 µ. The non-viable particles are the carriers for moving bacteria from one place to another. Particles smaller than 0.5 µ  are less critical because microbes are less likely to attach to these particles.

Particles bigger than 5 µ are too heavy to fly. hence when microbes are attached to particles, particles settle down on the floor. This is the reason why 0.5 µ and 5 µ  particle size is being monitored.

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What are the HEPA filter classification and Filter Ratings?

The below-mentioned table provides the details of HEPA filter classification.

CEN. EN - 779	Eurovent Class 4/5	EA < 20% Average Arrestance	EA £   20% Average Eff.	Filters Group	Micron rating
G1	EU. 1	65%	-	Coarse filter	-
G2	EU. 2	65  to 80%	-		-
G3	EU. 3	80  to  90%	-		20
G4	EU. 4	90  to  95%	-		10
F5	EU. 5	95  to  97%	40  to  60%	Fine filter	5
F6	EU. 6	97  to  98%	60  to  80%		5
F7	EU.7	98  to 99%	80  to  90%		3
F8	EU. 8	Semi HEPA	90  to  95%		0.3
F9	EU. 9	Super semi HEPA	95  to  98%		0.3

Sr. No	Eurovent Class	Initial Eff. Ei%	Penetration rating	Micron	Filter Class
1	EU. 10	95 to 99.9%	5/ P > 0.1	0.3	HEPA
2	EU. 11	99.9 to 99.97%	0.1 / P> 0.03	0.3	HEPA
3	EU. 12	99.97  to 99.99%	0.03 / P > 0.01	0.3	HEPA
4	EU. 13	99.99 to  99.997%	0.01 / P > 0.001	0.3	HEPA
5	EU. 14	99.999%  to 99.9995%	0.001 / P	0.3	HEPA
6	EU. 15	99.9995  to 99.9999%	-	0.12	ULPA
7	EU. 16	99.9999  to 99.99999%	-	0.12	ULAP
8	EU. 17	99.99999  to 99.999995%	-	0.12	ULPA

Conclusion of HEPA filter:

For an effective cleanroom environment, HEPA filter classification is more important. This is required to maintain aseptic conditions in the cleanroom areas. Hence while designing an HVAC system, a suitable HEPA filter has to be selected based on cleanroom requirements.