Grade of filters used in depyrogenating tunnel

Dear All,
Pls guide me why we are using EU-13 grade HEPA filter in Heat zone but in cooling and drying zone we are using EU-14 grade HEPA filter depyrogenating tunnel.


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Technically speaking the Heating zone will be operational at a temperature of 310C and above and then the conveyer moves to depyrogenate the incomming Vials/Ampoules. In such casses any microbes that might be entering the Heating zone will be killed or denatured or incenerated in no time. Even spores are killed in less than 1 minit.In such event you need to have a filter that sustains heat, prevent about 95% of bacterial and about 99% no-viable particle ingress.

On the other hand when the conveyer moves into cooling zone it is in a critical area. The filters should have an Filtration efficiency of not less than 99.97. In this you have a 5 micron prefilter that takes air from your class 10000 where you house your Deyrogenating Tunnel and that air enters thru the HEPA filter. The quality of air used to cool such sterile Deyrogenated air should be having same chareterestics as CLASS 100 in the Filling zone. If such filters are not housed on to your Tunnel the Sterilitry Assurance Level (SAL) of Vials are compromised and they contaminate the product during filling operation.

The drying zone is an area where the vials after washing enters into the tunnel. This is an area where they are preheated from the exhaust air of tunnel.This is a critical point so that they will not be exposed to external or particulate matter.

All these filters are installed by Depyrogenating Tunnel manufacturers as per CGMP guidance to assure the sterility of operations and also ensure prevention of any external non-viable particulate matter once they enter such deyrogenating systems.


Dear Durga,

I want to know if inthe depyrogen area is obrigatory to have a HEPA filtration for the air or only in the entrance area and in the cooling area is necessary??

Wich tests are necessary to qualify the air of the tunnel?? do you have any specification of air flow test to tunnel??



HEPA filters are necessary(Regulatory obligation) and essential in following zones in a tunnel sterilizer:

At Entrance where Vials enter after washing
Pre heating Zone
Cooling zone

It is obligatory to protect vials once they are washed.

The following tets are conducted at all HEPA filters in a Tunnel sterilizer:

Integrity Test with Poly alpha oleiphin–Praticulate generator

Air velocity measurements at 5 points ( 2 left corners, 2 right corners, 1 centre) at a distance of 15 to 30 centimeters max.

Air flow patterns for all HEPA filters and photographs or vedios must be recorded and kept

After the above–Clean the cool zone with 0.1% phenol , later with IPA 70% & with 0.5% Cetrimide ( always use freshly collected and cooled WFI to make solutions) and run the cool zone and tunnel conveyer for 45 minits . Stop the conveyer and expose atleast 11 settle plates on the cooling zone.

You must have less than 0.1 bacterial colony per plate.

This is the essense of HEPA.

Any further doubts please ask.We are here to clarify all doubts with in 12 hours.


Key parameters to be noted
Positive pressure to entrance
Even distribution of heat
Belt speed recorder
HEPA-filtered cooling air
Exhaust HEPA filter
Heater current
Particulate control

Dear Durga,

Thanks for the answers.

My doubts are:

In my company we have a tunnel by radiant heat and dont have HEPA filter in the depyrogenate area. Its used Nowadays??



In depyrogenation area there will be no Filters.You are right.That area is having the heating fillaments and an exhaust.
It operates at 305+C so no need of filters.

which tests i need to do in the chamber of depyrogenate area?? particle count (with operate temperature?? 340 degrees)…etc…

Iam really sorry about my last post.There will be HEPA filters over the heating elements. You need to perform the particulate counts when the depyrogenation zone is not in operation. The HEPA filters in this zone normally comes installed from factories. In other zones you need to install them at the site of operation . During installation all the tests that were mentioned in above posts should be carried out.

Carry the test when you do not operate the deyrogenation zone.

My preoccupation is that in the company that i work, auditors said that HEPA filter in the hot chamber is now obrigatory, but i didn`t found standards that mention it.

Do you have articles/standards about this topic?? can you send me in these emails??



It follows same standards such as Dry Heat Sterilizer. The reason of HEPA is that after the heating elemnts cools down it might suck air from external environment and it might increase bioburden. Even if you keep your Tunnel in class 10000 it is an obligatory requirement.I will try to find out the regulations and send you a mail.

We can prove only microbiologic by the temperature but phisical particle not. The positive pressure differential inside the tunnel is very important in this case, ok??

You can conduct studies by inoculating vials with spores of Bacillus var niger. This can be done once during the installation. This test need not be repeated. The purpose of thermal validation is to demonslrate that heat is uniformly delivered to all parts of the oven or tunnel load. The principles fot tunnels and DHS same as for autoclaves.

For endotoxin destruction. items must be spiked with bacterial endotoxin and passed through preferably shortened (for tunnels this means faster belt speeds than specified) or cooler cycles than the proposed process specification.

The spiked items should be placed in previously identified cold spots. They are then retrieved and assayed by the LAL method for remaining traces of endoloxin.You should always spike with 1000 times more load of endotoxin than the detectable limits in this validation operation.

You cannot prove a positive pressure in the sterilizing zone. Its rather difficult.

I give you a small guidance here for you how air should flow

Cool zone towards Hot zone
Drying zone or entry to Hot zone
Air from Class A must flow into the tunnel cool zone.

The Laminar flow CFM on the vial filling line must be higher than the CFM measured on the cool zone of the tunnel.

Class 10,000 air must be prefiltered and sucked by HEPA of the tunnel thus reducing both bioburden and particulates in the air.