Temperature Mapping is performed to determine if a storage area can maintain temperature within defined limits (Fridges, Freezers, Rooms, Warehouses and Incubators etc.). Sensors are distributed throughout the unit/room in pre-defined locations to confirm it performs within pre-defined set points.

The storage area is further challenged with additional tests such as empty mapping, loaded mapping, door open, power failure, pull down tests, fan failure etc. which are all performed to demonstrate the unit controls within pre-defined parameters and to determine the position of permanent monitoring/alarm probes.

What set point should we use?

​The table below lists some common laboratory instruments and their set points:

 

Picture​These temperature set-points are used as an initial guide, however if temperature mapping demonstrates a more suitable set-point for the range then the set point can be adjusted (e.g. 31.9°C instead of 32.5°C may provide a more uniform temperature within the specified limits due to the location of the control probe).

What tests should we perform during Temperature Mapping?

For temperature controlled units such as fridges, freezers and incubators, the testing required should be identified during risk assessment. Examples of common tests performed include:

  • Temperature Distribution Test (Empty)
  • Temperature Distribution Test (Loaded)
  • Door Open Test
  • Power Off Test


Additional tests that may be performed if required for the product or process:

  • Temperature Distribution (Partial Load)
  • Temperature Penetration Test (Loaded)
  • Pull Down Test

For some storage environments, for example warehouses, it may not be possible to perform some of the testing for example an empty distribution map, power off or door open. There may also be additional testing requirements specifically for that environment which could include:

  • Compressor Switch over Tests
  • Compressor Failure Tests

How long should we map for?

​The duration of temperature map should show the stability of the unit and identify any routine changes within the use for example a defrost cycle. Your site may already have a Validation Master Plan (VMP) or procedure with the mapping durations detailed. The table below shows some typical examples for temperature mapping durations:

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​For warehouses it is important to consider the movement of people, fans, doors opening and closing, seasonal variations. It is important to consider the impact of these variations including changes in shift patterns or the week and weekend. It is also important to understand the temperature distribution during seasonal variations by performing winter and summer maps.


How many sensors should we use for temperature mapping

​The number of sensors required really depends on the type of unit being tested and what it will be used for. Some common examples of number of sensors can be found below:

Fridges, Freezers and Incubators (Temperature Controlled Units)

  • Under bench Units                                              9 Sensors
  • Upright Unit                                                       12 Sensors

Cold Stores – Based on a risk assessment which would consider:

  • Unit Size
  • Fan Location
  • Vent Location
  • Racking/Shelving

Warehouse – Based on a risk assessment which would consider:

  • Size of warehouse
  • Fan Locations
  • Heater Locations
  • Air Conditioning units
  • Windows/Skylights
  • Racking and Shelving
  • Internal and external doors

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Where should we place our sensors

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​Sensors should be distributed throughout the storage area to get a detailed understanding of the performance of the unit. To identify cold/hot spots within the unit/area and determine locations for the permanent monitoring probe/s.

If this is a requalification exercise a sensor should be placed ajacent to the monitoring/alarm probe/s. This is to ensure that this location is the most suitable for the monitoring probe i.e. the Highest or Lowest temperature within the unit.

A common mistake is to place the monitoring probe in the location closest to the averarge temperature within the unit. This is the location least likely to fail, this would mean that any fault with the system is unlikely to be detected unit the next requalification exercise.

We recommend that two moitoring/alarm probes are placed with a temperature controlled unit. These probes should be located in the minimum and the maximum temperaure locations identified during the temperature map. This will help identify any faults with high and low temperatures on the unit.

Monitoring probes maybe placed in suitable buffers (Glycol, aluminum block etc) or with alarm delays to prevent regualr alarms caused by routine use (door opening etc.)


Should we be mapping humidity?

​​We perform humidity mapping on storage areas that contain product which may be impacted by a change in humidity, stability cabinets and humidity chambers. Humidity should form a part of the risk assessment to determine if monitoring and mapping is required.

When performing humidity mapping it is important to ensure the humidity data loggers are calibrated for the range you are testing.

Humidity Mapping Dataloggers VL-2000 Vaisala


What data logger should we use for temperature mapping?

​Data logger cost vary from around 10€ up to several thousand pounds, the quality differences between these loggers is substantial. The quality and accuracy of the loggers increase with the cost and some loggers are not suitable for certain applications.
Some important considerations are:

  • Accuracy
    • This can vary between ±2°C to around ±0.05°C and is dependent on use.
    •  Equipment at Thermal Compliance, accuracy range varies from ±0.05°C to ±0.5°C depending on application.
  • Response Time
    • This will impact the data received, probes with slow response times will artificially buffer fluctuating data.
    • Note: Response Time is very important for sterilisation processes and EN285:2015 requires the sensors Response Time (T-90) to be ≤5 Seconds. We anticipate this will become more prevalent in other sterilisation standards.
  • Internal /External Sensor
    • Internal Sensors create an air buffer and this has an impact on the data measured. Essentially they may not record the highest and lowest temperatures.
    • External Sensors are in free space and this can aid the placement of the sensor. They can also be used for product penetration tests.
  • Materials of Construction
    • Stainless Steel (For Cleanrooms)
    • Consider if the logger is to be used in an ATEX Area
  • Logging frequency
    • What is the minimum frequency you require to log, for example a freezer is normally mapped with a 10 second – 1 minute interval however for autoclave validation a 2 second log interval maybe more appropriate.
  • Memory Size
    • How many logs/data points can you record, this should be suitable for the duration and log interval of your temperature mapping exercises. If you are logging at 1 minute intervals for 24hours this would be 1440 data points. If however you were logging at 2 second intervals for a 24hour mapping exercise you would need 43,000 data points.
  • Range
    • Consider your site requirements, do you need to temperature map an Ultra Low -80°C Freezer, if you do then you will require a sensor that can record and has been calibrated below the temperature range for example -90°C.
    • Are you going to use the same loggers for high temperature processes? If so then you would need to ensure the logger is suitable for use at these temperatures.
  • Calibration
    • Can the logger be calibrated and is it possible to apply offsets?
  • Software
    • Ensure the software is 21 CFR Part 11 Compliant
    • Can the software meet your URS and your Installation Qualification (IQ) and Operational Qualification (OQ)
    • Is the software flexible enough to apply calculations and process complex data?
    • Can the software compile all data loggers to one graph to provide clear graphical data.

The sensors you choose should fit the process you’re looking to perform testing on. Whilst a high end data logger may meet the requirements for response time in an autoclave it is not ideally suited to temperature mapping a warehouse, which may require hundreds of sensors.

The data logger software is often overlooked when purchasing new sensors. Suitable software can offer substantial time savings in data processing, data review and quality assurance approvals. At Thermal Compliance even with our most cost efficient data loggers we use high end software to provide clear and compliant reports. Data loggers expedite the process of temperature mapping and suitable software expedites the documentation, reporting and review stages.