Climatic Chamber Configurator
Discover the Climatic Chamber Configurator
Our guide to choosing the climate chamber best suited to your needs.
Sterilization is a fundamental and indispensable process in many fields, especially in the medical-scientific field.
Nowadays, there are many methods to sterilize an object or an environment but one of the most effective remains hot air sterilization.
In the following article, we will take a detailed look at the various types of hot air sterilization, the international standards governing the procedures, and the best laboratory instruments capable of performing hot air sterilization.
What is Sterilization?
The history of modern sterilization dates back to the great Louis Pasteur, the father of microbiology who worked in the second half of the nineteenth century.
As humanity began to better understand the existence of microorganisms and their dangers, the need arose to develop a process that would completely eliminate their presence in very delicate activities, such as surgery.
But only in the following century, thanks to technological advancement , were the first true modern sterilization techniques developed , that is, the complete elimination of microorganisms from an environment or an object.
Today, a material is defined as sterile if the probability of finding a microorganism in it is less than one in a million.
Among the various contemporary methods we find hot air sterilization.
Types of Hot Air Sterilization
The first field of application of hot air sterilization is the medical-scientific, both to create an environment suitable for the growth of cultures and to sterilize medical instruments.
There are two types of hot air sterilization, both very common.
We speak of moist hot air when we act by means of flowing or saturated steam, with instruments such as the Koch pan and theautoclave.
Typically, the temperature to be reached with this method is 90° and the procedures are regulated by the ISO 17665-1:2006.
Dry hot air sterilization , on the other hand, requires much higher temperatures.
Generally, a temperature of 160°C (320°F) must be reached for one hour or 180°C (340°F) for 30 minutes. The specific procedures are outlined in ISO 20857:2010 .
Dry hot air sterilization is performed using ovens, dryers, incubators, and environmental chambers.
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FDM Ovens for Hot Air Sterilization
FDM – Environment Makers has been manufacturing laboratory instruments for over 70 years and, when it comes to dry hot air sterilization, we have two different products that perform this function.
On one hand, there are FDM ovens and dryers, specialized in temperature control and capable of reaching extreme values such as 300°.
On the other hand, there are FDM environmental chambers that reach 180° (perfect for the standard procedure) but have many other functions including controlrelative humidity and can be equipped to carry out most climatic tests.
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Reference Standards
- ISO 20857:2010 — Sterilization of health care products – Dry heat. Requirements for development, validation and routine control of a sterilization process.
- ISO 17665-1:2006 — Sterilization of health care products – Moist heat, cited for comparison and general process requirements.
- EN 285:2015+A1:2021 — Sterilization – Steam sterilizers – Large sterilizers, reference for thermal chamber design.
- ISO 11138-4:2017 — Sterilization of health care products – Biological indicators Part 4: Dry heat (Bacillus atrophaeus ATCC 9372).
- ISO 11140-1:2014 — Sterilization of health care products – Chemical indicators, Part 1 classes 1-6.
- USP — Sterility Assurance of Compendial Articles, American Pharmacopoeia.
- Ph. Eur. 5.1.1 — Methods of preparation of sterile products, European Pharmacopoeia.
Authoritative Sources
- ISO/TC 198 – Sterilization of health care products. ISO technical committee responsible for the ISO 17665, 20857, and 11138 series.
- EMA – European Medicines Agency. The European Medicines Agency publishes GMP Annex 1 guidelines on sterilization.
- FDA – US Food and Drug Administration. American regulator with 21 CFR Part 211 on pharmaceutical product sterilization.
- PDA – Parenteral Drug Association. International association with technical reports (TR 3, TR 48) on dry heat sterilization.
Frequently Asked Questions about Hot Air Sterilization
Which time-temperature combinations are validated for hot air sterilization?
ISO 20857 and pharmacopoeias recognize different time-temperature combinations to achieve SAL (Sterility Assurance Level) ≤ 10-6. The most commonly used cycles are: 160 °C for 120 minutes, 170 °C for 60 minutes, 180 °C for 30 minutes, 250 °C for 30 minutes (the latter for depyrogenation of pharmaceutical glassware, endotoxin reduction ≥ 3 log). The times refer to the plateau after all load points have reached the set point temperature; the heating-up and cooling times must be excluded. The critical parameter is the FH, time-temperature integral with reference 170 °C and z-value 20 °C typical for dry heat. For depyrogenation cycles, FH ≥ 3 min at 250 °C guarantees 3-log endotoxin reduction. Validation requires three consecutive cycles with B. atrophaeus bioindicators (≥ 6 log reduction) and thermal mapping with a minimum of 10 probes distributed in the load.
How is the thermal qualification of a dry chamber performed?
The qualification follows the IQ/OQ/PQ in compliance with GMP Annex 15. IQ (Installation Qualification) verifies installation, documents, calibrated instrumentation, and utilities. OQ (Operational Qualification) includes thermal mapping of an empty chamber with a minimum of 9 sensors according to ISO 17665-2 (geometric grid + center + corners), tests at three set points (160/170/250 °C), spatial uniformity calculation (max-min ≤ 15 °C in standard chambers, ≤ 5 °C in high-end chambers), and temporal stability. PQ (Performance Qualification) performs three consecutive cycles with maximum and minimum load, bioindicators (B. atrophaeus spores 106 CFU), class 6 chemical indicator, and integrated thermal probes in the most unfavorable products (cold spots identified in OQ). The instrumentation must have an uncertainty of ≤ 0.5 °C and be calibrated by ACCREDIA. All reports follow pre-approved protocols with pre-defined acceptance criteria.
What are the risks of incomplete depyrogenation?
Depyrogenation removes heat-resistant lipopolysaccharide (LPS) bacterial endotoxins that resist steam sterilization. An incomplete process at 250°C can leave endotoxins in vials, caps, and ampoules for injections, causing pyretic reactions in patients. The reference test is LAL (Limulus Amebocyte Lysate) pre/post process with a threshold of 0.25 EU/mL for injectable solutions. The main failure risks are: insufficient cold-spot mapping (spots < 250°C during plateau), oversized load blocking laminar airflow (forced convection required 0.5-1.5 m/s), residual condensation from previous cleaning, and contamination, particularly from degraded silicone seals. Revalidation is performed annually, plus any process/product/chamber changes. The challenge test with standard endotoxin E. coli O113:H10 (10,000 EU) must demonstrate ≥ 3-log reduction.
What characteristics should a hot air sterilization chamber have?
The chamber must guarantee a temperature range of up to 300 °C with uniformity ≤ ± 5 °C (≤ ± 2 °C for pharmaceutical GMP), forced convection air flow 0.5-1.5 m/s to ensure rapid thermal equilibrium, ramp ≥ 3 °C/min to minimize heating-up. Construction in AISI 316L stainless steel with internal electropolishing , insulation with high-temperature mineral wool, VMQ (silicone) gaskets resistant to 250 °C. HEPA H14 air filtration system (99.995% efficiency on 0.3 µm particles) for ISO 5 cleanchamber environments. Independent PID control with sensor redundancy (dual Pt100 class A). 21 CFR Part 11 audit trail with electronic signature, cycle backup on server, integrated printer. Multi-threshold alarms for overtemperature, door opening, fan failure. Interlock door (opening blocked during cycle). FDM tunnel and batch-type depyrogenation chambers support volumes of 200-2000 L with pre-validated pharmaceutical cycles compliant with EMA Annex 1 and FDA 21 CFR Part 211.
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