Dairy Establishment Inspection Manual – Chapter 19 Appendices
Appendix 10 Preventing Cross Connections in Dairy Plants

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The proper separation of pipelines in dairy processing plants is important to assure the safety of finished products. Improper separation of pipelines has been a factor in the outbreak of milkborne illness in the past.

A cross connection is a direct connection allowing one material to contaminate another. There needs to be a complete segregation of incompatible products such as raw materials and pasteurized or sterilized food products, cleaning products and food products, and waste materials or utility materials and food products.

For acceptable segregation between raw and pasteurized or sterilized dairy products refer to the specific requirements in Chapters 11, 12, 13, 14 and 17.

For other applications CIP (clean in place) supply lines and return line circuits used for CIP cleaning and mini-washes on tanks, lines, pasteurizers or other equipment that may be washed while connected to product lines containing milk products or potable water and lines for final rinse), this segregation must be accomplished by the use of separate pipelines and vessels for incompatible products and establishing effective physical breaks at connection points by at least one of the following arrangements: physical disconnecting of pipelines, double block and bleed valve arrangements, double seat (mix proof) valves, aseptic barriers, or other equally effective systems.

Flow diverter boards and "swing elbows" are traditionally used in dairy plants to isolate cleaning circuits, preventing contamination of food products with cleaning solution; this provides a physical break (disconnection) between pipelines. The installation of any number of segregating valves (set of valves with no break to atmosphere) does not constitute a physical break and is not acceptable, except in the following cases:

1. Special Case - Double Block and Bleed Valve Arrangements for CIP Cleaning

A double block and bleed valve arrangement with a self-draining (vent or leak port) break to atmosphere of at least the same hydraulic diameter as the largest supply line to the valves, located in between the two blocking valves, may be used to separate approved cleaning solutions from food products.

The blocking valves are used to act as a barrier to the product and the CIP solution, while the bleed line between them prevents the build-up of pressure and allows any leakage to be safely diverted away from the opposing valve seat.

The valves used for the double block and bleed must use micro-switches or other sensors to signal that the valves are properly positioned for CIP cleaning. The valves must move to the fail-safe blocking position with the bleed line open if air pressure or electrical power is removed from the valve solenoids.

Cleaning of the vent area or leak port in double block and bleed systems can be a problem. The design and installation of the vent/leak port must be such that the vent cleans properly by CIP methods. Cleaning of the vent/leak port can only take place when food products are isolated further upstream by another block and bleed valve set, flow board or swing elbow, or when food product has been removed from the system.

Procedures for the proper set-up, validation, maintenance, inspection and cleaning of this valve arrangement must be documented. There must be documentation in the plant's files (or access to the electronic records) that the procedures are followed in daily operations to prevent the contamination of dairy products with cleaning chemicals.

2. Special Case - Double Seat (Mix Proof) Valves for CIP Cleaning

A double seat (mix proof) valve may be used to separate approved cleaning solutions from food products. This valve must have two seats with a leakage chamber (vent or leak port) between them. The leak detect vent must always be fully open to the atmosphere unconnected with no restrictions and the valves installed such that a leak can be observed, and that the valves fail safe position is defined as closed. The leakage chamber must be vented to the atmosphere with a leak detect tube having a hydraulic diameter greater than the hydraulic diameter of the supply. (The hydraulic diameter can be defined as 4 × cross sectional area/perimeter. The supply cross sectional area is the perimeter of the seat multiplied by the travel of the seat lift, or where both seats are closed, it is the separate CIP supply port; the leak detect tube hydraulic diameter is the smallest of diameter in the leak tube).

Plant management must ensure in conjunction with their valve supplier/manufacturer that valves used in their system are suitable for the intended purpose and meet the minimum requirements of Appendix 10. This must be demonstrated to the authorities through testing, validation and proper documentation.

The double seat (mix proof) valve must use at least one micro-switch or other sensor to signal that the valve is properly positioned for CIP cleaning. The valve must be closed (inactivated position) for CIP cleaning and only one seat lifter at a time can be activated. The seat lift travel must be physically limited by design. Valve sequencing shall be done in such a manner that the two sides cannot open at the same time. The plant is responsible for maintaining test results on file for the micro-switch or sensor inter-wiring with CIP controls and the fail-safe positioning of the valve actuators. There can be no uncontrolled manual override of the system, and limited access to valve programming by unauthorized personnel/employees.

Cleaning of the vent area or leak port in double seat (mix proof) valves does not pose the same cross contamination potential problem as for double block and bleed valve arrangements. The vent is always open to atmosphere, but the flow is restricted by the annular space formed by the gap between one of the two seats and body, the plungers and the valve seat and stem. For example, cleaning of the valve vent area can be done in two ways. One cleaning practice is to perform individual seat lifts to allow some CIP solution to flush past and wash the product contact surface. The second option is through the use of an external CIP connection to the cavity. With the latter option the external CIP connection must meet the hydraulic diameter criteria as outlined above.

The use of the double seat (mix proof) valve must be managed through proper valve selection, set-up, validation and maintenance inspection. There must be documentation in the plant's file (or access to the electronic records) that the procedures for these double seat mix proof valves are followed in daily operations to prevent contamination of dairy products with cleaning chemicals. During indepth inspections, random inspections by the inspector, representative of the plant's valve system design should be performed to give an indication of the mechanical state of repair (e.g. based on a 25% frequency of sampling, all the valve clusters would be reviewed as a whole every 4 years). In a larger more complex plant, a targeted inspection of critical valves within a valve cluster could be done to give an indication of the mechanical state of repairs. In addition to the random inspections, the inspector should also be reviewing the plant=s documentation for deficiencies, trends and to ensure that proper maintenance is being maintained or increased maintenance frequency has occurred when necessary.

Double-seal type valves may not be used for this application because they use only a single valve actuator and rod and are not designed to safely vent significant quantities of leakage away from an opposing valve seat.

3. Cleaning Aseptic Processing and Packaging Systems (APPS)

An aseptic barrier may be used to segregate cleaning solutions from sterilized milk products during CIP, mini-washes or pre-sterilization of an aseptic surge tank or aseptic filler and associated piping in the aseptic zone.

In the case of sterilized product in the aseptic zone of an APPS, an interlocked resistance thermal device (RTD) monitoring leakage in one or more steam blocks would take the place of the break to atmosphere and valve micro-switches described above. An aseptic barrier can include one or more steam blocks, but must include a resistance thermal device (RTD) or other acceptable temperature sensor at the lowest level of the barrier to detect any fluid leakage into the barrier. If leakage is detected by the temperature sensing device, an alarm or other appropriate system must alert the operator to the aseptic barrier failure. Appropriate action as indicated by the scheduled process deviation procedure must be followed.

Cross Connections - Plant Management Responsibility

Plant management is ultimately responsible for the safety of the finished product and that includes the responsibility to ensure that equipment and/or pipelines are not installed or operated in a manner that will jeopardize the safety of pasteurized or sterilized product, or the integrity of CIP systems. Plant management must thoroughly review all proposed installations, and advise the dairy plant inspection authorities of intended changes.

Colour coding of pipelines on the plant schematic (or Process and Instrumentation Drawing (PID)), or use of the envelope method, may help to identify cross-connections in the piping between raw and pasteurized or sterilized product, cleaning products and food products, and waste materials or utility materials and food products. Cleaning and operating procedures must also be reviewed to make sure that these procedures are not creating a cross-contamination risk. The plant needs to maintain a listing of all cleaning chemicals and other non-food chemical products used at the plant, and these chemicals must be listed on the Canadian Food Inspection Agency (CFIA) accepted materials listings.

Cross Connections - Government Responsibility

Plant changes to piping, pasteurizers or sterilizers must be reviewed by dairy plant inspection authorities. Compliance with Federal and Provincial Regulations, and conformance to the Dairy Establishment Inspection Manual (DEIM) guidelines must be checked, and findings documented.

Cross connections are evaluated under DEIM tasks 1.10.01.02 Plant Blueprints and Process Flow, 1.10.05.02 Plant CIP System, 1.10.05.03 Truck/Raw Product CIP System, 1.11.01.02 No Cross Connections (High Temperature Short Time - H.T.S.T.) 1.14.01.02 No Cross Connections (APPS) and 1.17.01.02 No Cross Connections (Higher Heat Shorter Time and Extended Shelf Life - HHST/ESL). A physical verification shall be done on piping to verify if the schematic is accurate and if in actuality, no cross connections exist. Even if the plant does not have a schematic on file, an assessment for cross connections must be completed by inspection personnel.

Plant cleaning procedures and practices also need to be verified to determine if proper procedures are being followed, especially in regards to a CIP mini-washes being done on pasteurizers, sterilizers, or other equipment where product could be contaminated by cleaning solutions through improper procedures or equipment hook-up. Cleaning procedures and practices are evaluated under tasks 1.10.04.02 Flow and Practices, and 1.10.05.01 Sanitation Program General. Cleaning chemicals in use must be on the CFIA accepted materials list, as outlined under DEIM task 1.10.02.08 Non Food Chemicals.

Cross Connections- Appendix 10
Table description

This table shows the tasks and inspection criteria to evaluate cross connections

Task Inspection Criteria

Evaluated for:

1.10.01.02
1.10.05.02
1.10.05.03
1.11.01.02
1.14.01.02
1.17.01.02

(A) Physically verify piping and valves on site

(B) Free of cross-connections between cleaning/non-food materials and food products

1) Segregation

  • separate vessels, pipelines, valves
  • physical breaks at connections

2) Disconnection

  • flow divert boards
  • swing elbows

3) Double Block and Bleed Valves

  • Vent or Leak Port
    • hydraulic diameter of largest supply line to valves
    • vent cleaned only when food products physically/totally isolated
  • Valves
    • micro-switches or sensors to signal fail safe position during CIP cleaning
  • Documentation
    • procedures for set-up, validation, maintenance, inspection and cleaning
    • records that procedures are followed daily

4) Double Seat (Mix Proof) Valves

  • Leakage Chamber
    • leak detect tube ≥ hydraulic diameter of largest seat lift or external CIP connection to the leak chamber of the valve
    • must always be fully opened to atmosphere (unconnected no restrictions)
    • must be visible for leak detect
  • Valves
    • micro-switch or sensor to signal fail safe position during CIP cleaning
    • one seat lift at one time
    • mechanically limited seat lift
  • Documentation
    • procedures for set-up, validation, maintenance, inspection and cleaning
    • records that procedures are followed daily
    • test results for micro-switch/sensor interwiring with CIP controls and fail-safe position of valve actuators

5) APPS

  • Aseptic Barrier
    • one or more steam blocks
    • resistance thermal device (RTD) or temperature sensor
    • alarm or indication of barrier failure

Hydraulic diameter

The hydraulic diameter, dh, is used instead of the geometrical diameter for channels of non-circular shape. dh is defined as:

dh = 4 × cross-sectional area ÷ wetted perimeter

For different geometries dh becomes:

  1. Circular Tube: dh = 4 × Π × d2 ÷ 4 ÷ Π × d = d; dh = d
  2. Square Tube: dh = 4 × a2 ÷ 4 × a = a; dh = a
  3. Two Concentric Tubes: dh = (4 × (Π × D2 - Π × d2) ÷ 4) ÷ (Π × D + Π × d) = D – d; dh = D − d
Figure 1: Dimensions to calculate the hydraulic diameter
Figure 1: Dimensions to calculate the hydraulic diameter. Description follows.
Description for image - Figure 1: Dimensions to calculate the hydraulic diameter

This figure illustrates the diameter of circular, square and concentric tubes that is used in equations to determine the hydraulic diameter of the tube.

d = diameter of circular tube or the inner diameter of concentric tubes

a = the width of the square tube

D = outer diameter of two concentric tubes, Hydraulic diameter equals four multiplied by the cross sectional area divided by the perimeter

Hydraulic diameter equals four multiplied by the cross sectional area divided by the perimeter

  • Circular Tube: Hydraulic diameter equals four multiplied by pi multiplied by the square of the diameter divided by four divided by pi multiplied by the diameter equals the diameter; Hydraulic diameter equals the diameter
  • Square Tube: Hydraulic diameter equals four multiplied by the square of the length divided by four multiplied by the length equals the length; Hydraulic diameter equals the length
  • Two Concentric Tubes: Hydraulic diameter equals pi multiplied by the square of the outer diameter minus the product of pi multiplied by the square of the inner diameter the total of which is divided by four and then divided by the total of pi multiplied by the outer diameter plus the product of pi multiplied by the inner diameter equals the outer diameter minus the inner diameter; Hydraulic diameter equals outer diameter minus inner diameter

Hydraulic diameter and flow resistance

To compare runners of different shapes, you can use the hydraulic diameter, which is an index of flow resistance. The higher the hydraulic diameter, the lower the flow resistance. Hydraulic diameter can be defined as:

dh = 4A ÷ P

Where, dh = hydraulic diameter

A = cross section area

P = perimeter

Figure 2: Illustrates how to use the hydraulic diameter to compare different runner shapes
Figure 2: Illustrates how to use the hydraulic diameter to compare different runner shapes. Description follows.
Description for image - Illustrates how to use the hydraulic diameter to compare different runner shapes.

This image shows the hydraulic diameter for a hexagon (0.9523), a half-oval (0.9116), a square (0.8862), a trapezoid (0.8771), a half-circle (0.8642), a short rectangle (0.8356) and a long rectangle (0.7090).

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