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How to validate thermal covers?

Coolchain route qualification starts with risk assessment according to identified factors

Risk factors:

  • Time
  • Temperature
  • Handling
  • Payload size
  • Load density
  • Transit
  • Schedules
  • Network
  • Processes

Qualification Steps

  • DQ – not applicable
  • IQ – not applicable
  • OQ – applicable, static tests, normal & worst case conditions
  • PQ – applicable, dynamic tests during transport validation studies
  • OQ and PQ typically part of GDP process validation plan

Performance qualification

Importance of considering sun radiation and greenhouse effect when performing risk assessment

  • Sun radiation is a well-known cause of temperature spikes
  • It’s often ignored during operational or performance qualification and risk assessment
  • Transparent or clear stretch wrap can create greenhouse effect
  • Colored or black covers expose to heat absorption
  • White highly reflective covers protect much better

The science: Heat transfer mechanisms

  • Conduction – pallet reduces direct contact with hot floor – wood poor conductors
  • Convection – heat transfer from air is poor, closed bottom prevents convection
  • Radiation – main source of heat transfer
  • From ground around the pallet
  • From nearby hot surfaces
  • Mostly directly from the sun

Emissivity vs reflectivity

  • A lot of product literature confuses reflectivity and emissivity
  • Both are important, but different
  • Emissivity measure how easily surfaces absorb or emit radiation – lower is better
  • Emissivity and reflectivity are only equivalent if:
  • There is no transmission or you collect emitted or reflected light at all angles
  • Incident and reflected/emitted light are measured over the same spectrum
  • Emissivity meter works at around 10,000 nm wavelength, most reflectometers measure between 400 and 700 nm!
  • It’s important to consider effects of hot and cold air flows during risk assessment
  • Tyvek® thermal blankets protect often as well as metallized bubble wrap and decreases the effect of extreme cold

Summary outcome of summer transport validation run

  • This shipment for a validation has been booked as Pharma shipment: Transport and Storage temperature +15°C to +25°C to be performed in summer to Dubai
  • Despite higher ambient temperature of +40 deg °C upon arrival in Dubai, and the fact that a top shrink wrap was used on top of the ULD/PMC the load temperature never exceeded +25°C due to the reflective Tyvek covers
  • The period of lower control before departure from Dubai was the period which were closest to losing control of controlled conditions
  • The switch between freighter and passenger flight (PAX) highlights the need to understand the operational details to understand potential direct exposure if booking a dedicated pharma service or general cargo

 

The latest EU Good distribution practices (GDP) have extended regulatory measures to cover the CRT temperature band from origin to destination, others will update their GDP’s

Its essential to do a rigorous and thorough risk analysis and qualification process

because if an unacceptable temperature violation occurs it will be necessary to demonstrate that the qualification process was appropriate to the risks.