Surface area

If we are using two equipment for same process (i.e. 2 FBD of same make, capasity) then we shoud consider both equipment surface area or only one FBD surface area is enough?

my second querry is if drying is done in three lot then also surface area to be taken once only?

pls suggest.

Dear Nimesh,

if there are two alternative pieces of equipment, for the purposes of calculating the accepted contamination limits you have to choose the one with the biggest product exposed surface which will give you the most stringent limit per area unit. This is only true if they are true alternatives; if they are used in parallel (for two subbatches) you need to sum the two surfaces.

If the drying operation is performed in the same equipment in three subbatches, nothing changes in the calculation, because the same whole batch (sum of the three subbatches) made contact with the same surface, three times, but taking up the same contamination as if the whole batch made contact once. Rigurously speaking, this is only true if after the drying the batch is mixed, but a as matter of fact this is a condition to be considered a batch, per definition of batch.

Best regards


thaks alfred.

do you have any surface area calculator for the equipment

Dear Nimesh,

sorry, no. As far as I know, there is no other way to calculate the equipment surface than measuring each surface and using geometrical calculations, which may be approximations. By the way, this is the step where you may include and justify considerations why to include or not some surfaces, worst case approximations, etc.

To calculate the accepted limits per surface area, it is sufficient to take the big surface areas and perhaps add a 10% - 20% to be on the safe side (the percentage depends on how intricate is the equipment). If there are parts that are sampled entirely or sampled by rinsing, a more detailed surface calculation for these parts is needed.

Best regards


sir i want to vmp plan document from sites pl give some sites name there is documents provide:)

Hi alfred,

We are designing a cleaning validation protocol for new facility, presently we have only two products and naturally we have identified worst case. We are defining a acceptance criteria based on dose calaculation for each equipment separately, this is becaue our facilty is multiproduct and we want to avoid diffferent equipment trains. we will put the product mix for each equipment and decide on acceptance criteria for everyequipment. My question is is this aproach accetable or we should consider the cummulitive resudue impact?
Thanks in advance,


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Dear Harsh,

that is exactly the point. You cannot define it only by piece of equipment, because there is no accountance for the cumulation of residues. That is why everybody uses the shared equipment train.

Without knowledge of your expansion plans, with two products it is not complicated to perform the calculation with the shared equipment. For a bigger product portfolio, you may need to automate this calculation with a spreadsheet, which is possible but needs a careful design of that spreadsheet.

Best regards


Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra (objects with flat polygonal faces) the surface area is the sum of the areas of its faces. Smooth surfaces, such as a sphere, are assigned surface area using their representation as parametric surfaces. This definition of the surface area is based on methods of infinitesimal calculus and involves partial derivatives and double integration.

Surface area is the area of a given surface. Roughly speaking, it is the “amount” of a surface (i.e., it is proportional to the amount of paint needed to cover it), and has units of distance squared. Surface area is commonly denoted S for a surface in three dimensions, or A for a region of the plane (in which case it is simply called “the” area).