Type B vs Type N Autoclave — MFDS Part 1 MCQ

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ModerateMicrobiologyType B vs Type N AutoclaveMFDS Part 1

A primary care dental practice intends to sterilise pre-wrapped instrument packs and hollow, air-retentive instruments in a benchtop steam sterilizer. Which feature makes a validated Type B sterilizer suitable for these loads, unlike a Type N sterilizer?

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Correct answer: C — A vacuum stage removes air before steam penetrates the load

A Type B sterilizer uses a vacuum-assisted air-removal phase before steam exposure. Removing air permits effective steam penetration into air-retentive spaces and makes an appropriately validated Type B cycle suitable for wrapped loads and hollow instruments. In contrast, Type N sterilizers use passive steam displacement and are not appropriate for wrapped instruments. Passive displacement cannot be assumed to clear all air from lumens reliably. Suitability is not explained by a lower sterilizing temperature: effective steam sterilization depends on achieving validated time, temperature and pressure conditions throughout the intended load. Type B sterilizers still use steam generated from water, not dry heat or chemical vapour. The sterilizer cycle and load must remain compatible with both the sterilizer and instrument manufacturers' instructions.

Reference: NHS England. Health Technical Memorandum 01-05: Decontamination in primary care dental practices, paragraph 4.9, 2013. https://www.england.nhs.uk/wp-content/uploads/2021/05/HTM_01-05_2013.pdf