We use the 6-d rule as a "rule of thumb" for all systems, but we
test all deadlegs in SIP validations as sterile boundaries with BI strips of
I don't understand your point about not putting a small
diameter pipe on a large diameter pipe. We would consider only the
smaller diameter pipe's diameter and length.
We have found it is important to consider pipe slope and orientation
in steam sterilization. Even a short deadleg can present a problem if it is
located on the "bottom" of the pipe, or has a downward slope to the valve or
fitting at the end, due to condensate buildup. Upward sloping deadlegs
(such as vessel flanges) can have air pockets.
Our experience has shown that BI's are neccesary in steam
sterilizations, as thermocouple temperatures can be high (above 125°C) in
locations with condensate problems that prevent BI inactivation.
> -----Original Message-----
> From: Moderator [SMTP:email@example.com]
> Sent: Monday, January 04, 1999 10:05 AM
> To: PharmSciTech
> Subject: Dead-Legs
> What is a dead-leg?
> This is my second attempt to shed some light on this delicate issue. The
> first attempt did not result in any response at all. Any response is
> wellcome. I know there are people out there having opinions in this
> The definition in the LVP proposal from 1976 is still valid for many
> people. In § 212.49 (3) it is stated that pipelines in water systems
> "Not have an unused portion greater in length than six diameters of
> the unused pipe measured from the axis of the pipe in use."
> This is not practicable since it would not be possible to put a small
> diameter pipe (for example a sample pipe) on a large diameter pipe.
> Many people seem to have interpreted this as valid also for other
> applications (for example steam sterilizers) where piping is involved.
> With the technology available today even six times the diameter (6D) is
> hardly considered as cGMP for water systems.
> The reason for limiting the length of branching pipes is to avoid stagnant
> water, decrease in temperature and subsequent microbial growth. If this
> be proven during validation not to occur, would the FDA accept any length
> of piping?
> On a sterilizer ,where it often is impossible to achieve a piping less
> 6D because of insulation thickness and other physical limitations, is it
> permitted to have 6D or even longer? Here the piping can be fitted to
> back into the chamber, it is possible to draw a pre-vacuum to remove
> entrapped air etc.
> If it during validation can be shown that no microorganisms can survive is
> it then allowed to have 6D or longer?
> Which is the appropriate bioburden for a challenge test?
> Is it sufficient to use only temperature measurements for validation?
> I would be thankful if it is possible to shed some light on this very much
> debated topic. Thanks for your help.
> With best regards,
> GETINGE SCIENTIFIC
> Alf Gustafsson