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Drainage matters

04 March 2019

A whitepaper document offers guidance on hygienic drainage and its role in ensuring better performance in food manufacturing. Food Processing reports on some of the highlights of the document. 

To achieve high levels of hygiene and ensure product safety in a food and drink manufacturing environment it is critical to adopt best practice across all areas of manufacturing. Recent research and best practice guidance from a variety of academic bodies all recognised the importance of the infrastructure of a food/drink processing facility, and specifically the drainage.  

Research published in Applied and Environmental Biology, for example, highlighted that floor drains in food processing facilities are a particularly important niche for the persistence of listeriae and can be a?point of contamination in the processing plant environment and possibly in food products.  The research found that drainage is a critical component affecting the hygienic performance of food production. Effective drainage helps mitigate hazards from the external environment and is central to the safe and hygienic operation internally.

A properly specified drainage system will have a positive impact on hygienic performance, food/drink safety, employee health and safety, and operational costs so it is vital to consider drainage at the initial stages of a factory build or refurbishment.  If drainage is only treated as an afterthought then there will is a risk of having to rectify the drainage at a later stage in the build which is a costly task and could involve the removal of production equipment and floors, bringing considerable disruption to the manufacturing process.  

There are some key questions to ask yourself when specifying drainage  – Is your drainage fit for purpose; is it hygienically designed; and is it designed to be cleanable?

There are six key areas to consider to ensure a drainage system is fit for purpose:

1. Area of application
• Hygiene requirement / risk level
• Factory and equipment layout
• Fluid type to be drained

2. Grating requirements 
• Slip resistance
• Loading issues

3. Adequacy and hydraulic capacity

4. Installation and cleaning
• Floor/drainage connection
• Thermal shock loads
• Chemical attack

5. Maintenance requirements

6. Future proofing

Key questions that should be asked include whether the drainage is required in low, medium or high-risk areas? Whether line or point drainage is more appropriate, and what falls are required in the floor. Ask yourself whether the drainage system layout works in the context of the equipment being used? What hydraulic capacity is required? Does your application require 304 or 316 grade steel drainage? And is your choice of drainage and flooring future-proofed? 

Best practice
It is important to choose a drainage system designed in accordance with the best practice design principles of the European Hygienic Engineering and Design Group (EHEDG) and should apply the standards reserved for food contact surfaces EN1672 and EN ISO 14159.   

The EHEDG principles of hygienic design require channels to have completely drainable sumps and a minimal slope of 1% longitudinal and cross all areas. If your drainage isn’t fully drainable then its hygienic performance will be compromised. To optimise hygienic performance, drainage channels should have completely drainable dry sumps with engineered positive slopes to prevent the build-up of stagnant water, odours, microbial growth and potential chemical hazards. 

Does your chosen drainage solution feature lap joints and welded butt joints? EHEDG states that lap joints cannot be welded hygienically. When you weld a lap joint you create a void which will harbour bacteria. EHEDG guidelines also require all corners to be rounded. Sharp corners are harder to clean, particularly if they are situated at a right angle or bend in the drainage.  It is harder to get into a corner and to make contact with its entire surface, which means there’s a very real risk that the corner won’t get cleaned effectively.  To ensure every part of the drainage surface is easily accessible and to meet best practice guidelines, drainage should feature rounded corners with minimum radii of 3mm.  

Finally, do ensure that steel drainage is fully pickle passivated. Pickle passivation, is a process which is used to fully restore the all-important oxide layer that naturally occurs on stainless steel but is destroyed on welded joints.  Without this layer, stainless steel ceases to be corrosion resistant and that can affect a product’s lifespan as well as creating hygiene risks.  According to EHEDG Doc 18, it is essential that drainage is fully pickle passivated 

Cleanability is an important consideration. Ideally, drainage systems need to be designed to be fully cleanable, to make the cleaning process easy and to work practically with the cleaning protocol of a manufacturing facility.   

Another factor to consider is power-washing. This cleaning method will create a high-velocity aerosol spray that can travel and settle right across the process line, moving any bacteria living in your drains right around your facility. For this reason it is vital that drainage is designed in a way that does not make power-washing a requirement. 

One final point – drainage should never be considered in isolation. EHEDG states that drainage, cleaning processes and flooring should be considered holistically as they all directly impact upon the performance of each other.  In addition, drainage, cleaning and flooring are all prerequisites of an effective HACCP system. So, flooring and drainage must be compatible.   At the very least, the drainage design needs to connect properly with the surrounding flooring to minimise risks to hygiene. If the connection between flooring and drainage is not compatible and is not sound it can result in cracks occurring in the flooring immediately surrounding the drainage; elevation of floor plate edges; and delamination of flooring. These issues will compromise the performance of both the drainage and the flooring. 

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