---
title: "ASHRAE TC 9.9 Data Center Cleanliness and Humidity | Aethair"
description: "ASHRAE TC 9.9 data center guidance: ISO Class 8 cleanliness, humidity below 60 %, and G1 corrosion, with who it applies to and a recommended configuration."
url: https://aethair.io/standards/ashrae_tc99/
---

Compliance · ASHRAE Technical Committee 9.9

# ASHRAE TC 9.9: data center contamination and environmental guidelines

Indoor: data centers

ASHRAE Technical Committee 9.9 (Mission Critical Facilities, Data Centers, Technology Spaces and Electronic Equipment) publishes the environmental guidance data centers are designed and operated to. For contamination, it recommends keeping the white space at **ISO Class 8 cleanliness under ISO 14644-1 (3,520,000 particles/m³ at ≥0.5 µm)**, holding corrosive gases within **ANSI/ISA-71.04 severity level G1** (copper corrosion below 300 angstroms and silver below 200 angstroms per month), and keeping **relative humidity below 60 %** to protect circuit boards from corrosion.

[Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure ASHRAE TC 9.9 Monitoring](https://aethair.io/build/?params=particle_count,humidity)

At a glance

**ASHRAE Technical Committee 9.9** Indoor: data centers

2 parameters · 2 limit values

[Particle Count (by size)](https://aethair.io/parameters/particle_count/) [Relative Humidity](https://aethair.io/parameters/humidity/)

1 device measures them all

- **Aethair PRO**

[Official text from ASHRAE Technical Committee 9.9](https://tc0909.ashraetcs.org/)

Limit values

## ASHRAE TC 9.9 Limit Values

Every value ASHRAE Technical Committee 9.9 publishes for the 2 parameters below, with its averaging period, as the standard states it.

[**Particle Count (by size)** Particulate Matter](https://aethair.io/parameters/particle_count/)

**3520000 particles/m³** *ISO Class 8, ≥0.5 µm* the white space, per [ISO 14644-1](https://aethair.io/standards/iso_14644_1/)

[**Relative Humidity** Meteorology](https://aethair.io/parameters/humidity/)

**60 %** *Maximum* to protect circuit boards from corrosion

Who it applies to

## Who Uses It

Data center operators, colocation providers, and the equipment makers whose warranty conditions refer to the guidance, and designers of technology spaces. Particulate cleanliness is typically achieved with MERV 8 filtration for recirculating air and MERV 11 to MERV 13 for outside air.

Monitoring

## How Monitoring Supports It

Particles, temperature, and humidity can be monitored continuously in the white space and at the air intakes. The data shows when a filtration problem, nearby construction, or a humidity excursion puts equipment at risk. Corrosion severity is measured separately, with copper and silver reactivity coupons or corrosion monitors, because it is not a concentration any gas sensor reports directly.

[Customize this configuration](https://aethair.io/build/?params=particle_count,humidity)

### Who measures each parameter

| Parameter | Aethair PRO | Aethair IAQ | External |
| - | - | - | - |
| [Particle Count (by size)](https://aethair.io/parameters/particle_count/) | Built in | Built in | [1 instrument](https://aethair.io/parameters/particle_count/) via Thiamis |
| [Relative Humidity](https://aethair.io/parameters/humidity/) | Built in | Built in | [12 instruments](https://aethair.io/parameters/humidity/) via Thiamis |

Devices

## Devices That Cover ASHRAE TC 9.9

How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out.

Aethair monitors

[**Aethair PRO** Built-in sensors Covers both](https://aethair.io/products/pro/) [**Aethair IAQ** Built-in sensors Covers both](https://aethair.io/products/iaq/)

Covers both on its own

[**Particles Plus** Particulate & Dust Monitors](https://aethair.io/sensors/particles-plus-particulate-dust-monitors/)

Covers part of it (combine on one Thiamis)

[**Fluke Calibration 1620A DewK** Heat Stress & Comfort 1 of 2: Relative Humidity](https://aethair.io/sensors/fluke-calibration-heat-stress-comfort/)

Article Library

## Articles on ASHRAE TC 9.9

### [Data Center Air Quality Monitoring, Inside and Out](https://aethair.io/resources/data-center-air-quality-monitoring/)

Data center air quality monitoring for operators: ISO 14644 cleanliness in the white space, construction dust, generator emissions, and perimeter noise.

[All articles](https://aethair.io/resources/)

Questions

## ASHRAE TC 9.9 FAQ

What cleanliness does ASHRAE recommend for data centers?

ISO Class 8 under ISO 14644-1 for the white space, which is 3,520,000 particles per cubic meter at 0.5 µm and larger.

What humidity does ASHRAE TC 9.9 guidance call for?

Relative humidity below 60 %, to protect circuit boards from corrosion.

What is ISA-71.04 severity level G1?

The mildest corrosion class for gaseous contamination: copper corrosion below 300 angstroms per month and silver below 200 angstroms per month, measured with reactivity coupons or corrosion monitors.