Typical noise level of a ventilation fan At a distance of about 3 metres from a standard industrial ventilation fan, the approximate sound pressure level is:

Introduction / Context:
Ventilation and process fans are ubiquitous noise sources in plants. Estimating typical sound pressure levels at a few metres helps engineers decide whether to specify silencers, enclosures, or administrative controls. This question focuses on an order-of-magnitude selection consistent with common fan installations without special noise control.

Given Data / Assumptions:

• Standard industrial fan operating at nominal load.
• Free-field or semi-reverberant conditions at ≈3 m distance.
• No special silencers or acoustical enclosures fitted.

Concept / Approach:
Typical unsilenced fans produce broadband noise in the 80–95 dB(A) range at a few metres, depending on size, speed, blade-pass tones, and installation. Values above 100 dB(A) at 3 m are characteristic of much larger, high-speed or poorly designed systems. Levels near 125–145 dB(A) are extremely loud (near jet engine at close range) and unrealistic for a standard ventilation fan. Therefore, 85 dB represents a reasonable, widely cited approximate value for such a scenario.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer data sheets and textbook tables place many medium fans in the 80–90 dB(A) class at close distances without silencers; field surveys commonly confirm this range.

Why Other Options Are Wrong:

• 105 dB: Too high for a standard ventilation fan at 3 m unless unusually large or problematic.
• 125 or 145 dB: Unrealistic for typical plant ventilation fans; would indicate extreme sources.
• 65 dB: Too low for typical industrial fans in proximity without controls.

Common Pitfalls:
Assuming community noise values apply directly to near-field industrial equipment; distance and installation conditions matter.

Final Answer:
85 dB