Performing temperature mapping
Temperature mapping is performed by placing calibrated data loggers throughout a storage area for a period of time to study how temperature is distributed across the area.
The exercise will show whether the whole area is suitable for the storage of temperature sensitive medicines, identify potential risks and help to inform the placement of permanent temperature sensors.
Planning temperature mapping
Ensure that sufficient loggers are placed strategically to cover all points where medicines are stored, in ambient areas.
For example, place loggers in all the corners on the lowest and highest shelves, and some close to the middle of the room. Remember to include areas such as controlled drugs cupboards and medicines receipt or loading bays.
Identify any sources of hot or cold air such as heaters, lighting, windows and doors, and place additional loggers at the closest medicines storage point to these sources. It is usual to use between 8 and 25 loggers in an ambient location, depending on size and number of heat sources.
Refrigerator and freezer
The number and position of data loggers depends on the size of your fridge or freezer:
- for full size refrigerators and freezers, place loggers in each corner of the top and bottom storage shelves, and one in the middle of the middle storage shelf
- for under-counter and bench-top fridges and freezers the number of loggers can be reduced
- for double fridges and freezers, add one or two additional loggers in the middle
Refrigerators should be mapped full. This is to represent the worst case scenario for obstruction of air flow through the refrigerator. Ideally new fridges should also be mapped empty to establish baseline performance before they are stocked with medicines.
Freezers should ideally be mapped with their lowest stock holding or empty if possible. This is because frozen stock acts a ballast which stabilises internal freezer temperature.
Deciding on the mapping period
The mapping period needs to cover the storage area both in use and at rest. It should cover the highest use periods, e.g. big clinic days when a fridge is most full and has the most door opening.
The minimum length of mapping is usually 48 hours, however a longer period may be required to ensure it is representative of how the storage area is being used.
Initial ambient mapping exercises should be conducted during warm weather (summer) and cold weather (winter) to cover worst case scenario for extremes of temperature and variables such as heating or sun light entering through windows.
Mapping frequency should follow a risk-based approach, which considers the likelihood and consequence of a loss of temperature control. For example, ambient areas with no major changes to their structure of mechanical heating or cooling systems will require mapping less often than refrigerators or walk in cold stores used for storage of high cost drugs.
MHRA Inspectorate blog – Temperature mapping – an introduction