At what minimum temperature and time is dry heat sterilisation typically achieved in a hot air oven for sterilisation of glassware and metal instruments?

Explanation

## Dry Heat Sterilisation Parameters **Key Point:** Dry heat sterilisation requires **160–180°C for 1–2 hours** (or 170°C for 1 hour as standard) to achieve sterilisation of glassware, metals, and powders. ### Mechanism of Dry Heat Sterilisation Dry heat kills microorganisms through: 1. **Protein denaturation** — coagulation of microbial proteins 2. **Oxidative damage** — oxidation of cellular components 3. **DNA damage** — dehydration and damage to genetic material These processes require sustained high temperature over prolonged duration because dry heat penetrates slowly and is less efficient than moist heat. ### Standard Dry Heat Sterilisation Cycles | Temperature | Time | Application | | --- | --- | --- | | **160°C** | **1 hour** | Standard cycle for glassware, metals, powders | | **170°C** | **1 hour** | Alternative standard | | **180°C** | **30 minutes** | Shorter cycle at higher temperature | | 121°C | 15 min | **Moist heat (autoclaving)**, NOT dry heat | | 100°C | 30 min | Boiling — not sterilisation | **High-Yield:** The **160°C/1 hour** cycle is the most commonly tested standard for dry heat sterilisation in NEET PG. **Mnemonic:** **"DRY-160"** — Dry heat requires 160°C (minimum) for adequate sterilisation time. ### Why Dry Heat Requires Higher Temperature Than Moist Heat - Moist heat (steam) at 121°C for 15 min = sterilisation (water conducts heat efficiently) - Dry heat at 160°C for 1 hour = sterilisation (air conducts heat poorly; requires higher temperature and longer time) - Dry heat penetrates slowly through materials, necessitating prolonged exposure **Clinical Pearl:** Dry heat is preferred for items that corrode in steam (certain metals), absorb moisture (powders), or require no water residue.