ASTM E104-20a PDF

Full title and description

ASTM E104-20a — Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions. This practice describes a method for generating and maintaining constant relative-humidity environments in relatively small closed containers using selected aqueous (saturated salt) solutions; it includes ambient conditions, recommended salts (humidity fixed points), and safety notes for preparation and use.

Abstract

Provides a concise practice for producing stable relative-humidity environments (from very dry conditions up to near saturation) using saturated aqueous salt solutions. Applicable primarily to closed systems and calibration/conditioning applications over a practical temperature span, the standard includes guidance on solution selection, temperature considerations, and safety precautions for corrosive solutions and vapors.

General information

• Status: Active (current edition E104-20a).
• Publication date: Approved November 1, 2020; includes amendment/changes recorded December 21, 2020.
• Publisher: ASTM International.
• ICS / categories: Environmental testing; ICS code commonly cited: 19.040 (environmental testing / atmospheres).
• Edition / version: E104-20a (designation indicates 2020 revision with amendment).
• Number of pages: 5 pages (short practice document).

Scope

This practice describes one method to generate constant relative-humidity (rh) environments in relatively small containers and is applicable for obtaining fixed relative humidities from very dry to near-saturation at temperatures typically spanning approximately 0 °C to 50 °C. It is intended for closed systems such as environmental conditioning containers and for the calibration of hygrometers; it is not recommended for continuous flowing streams of constant humidity unless special precautions are followed to ensure source stability.

Key topics and requirements

• Use of selected aqueous saturated salt solutions (humidity fixed points) to establish reproducible RH values in a container headspace.
• Recommended temperature ranges and the importance of tight temperature control to realize expected RH values (typical application range ~0 °C to 50 °C).
• Applicability to closed test chambers and calibration enclosures, and limitations for flowing-air or continuous-stream applications unless stability measures are applied.
• Health and safety considerations: many saturated salt solutions are corrosive and may generate corrosive vapors — preparation, handling, and appropriate personal protective equipment are required.
• Reference tables of common salt solutions (humidity fixed points) and guidance on expected RH at given temperatures (table of HFP designations and salts is part of the practice).

Typical use and users

Used by laboratories and test facilities for conditioning specimens, performing shelf-life and stability studies, and calibrating hygrometers and other humidity sensors. Typical users include materials test laboratories, calibration/metrology labs, environmental-testing groups, research groups working with humidity-sensitive materials, and quality-control departments in manufacturing.

Related standards

Related documents and complementary standards include ISO 291 (standard atmospheres for conditioning and testing), ASTM D5032 (practice for maintaining constant relative humidity by means of aqueous glycerin solutions), and other ASTM documents referenced within E104 for terminology and reagent water specifications. Users often consult these documents together when establishing humidity-control procedures.

Keywords

relative humidity; constant RH; saturated salt solutions; humidity fixed points; hygrometer calibration; environmental conditioning; corrosion precautions.

FAQ

Q: What is this standard?

A: ASTM E104-20a is a short practice that describes how to produce constant relative-humidity environments in small closed containers using aqueous (saturated salt) solutions; the designation indicates the 2020 revision with a subsequent amendment.

Q: What does it cover?

A: It covers selection and use of saturated salt solutions to generate fixed RH environments, recommended temperature considerations (practical span about 0 °C to 50 °C), applicability to closed chambers and calibration tasks, and safety precautions for corrosive solutions and vapors. It also includes tables (humidity fixed points) for commonly used salts.

Q: Who typically uses it?

A: Calibration and metrology laboratories, materials-testing and environmental test facilities, researchers handling humidity-sensitive samples, and quality departments that require controlled humidity for conditioning or testing.

Q: Is it current or superseded?

A: The documented edition is E104-20a (approved November 1, 2020, with amendment activity noted December 21, 2020). Users should check the official ASTM publication or document listings to verify whether a later revision or reapproval has been issued since 2020.

Q: Is it part of a series?

A: E104 is a long-standing ASTM practice (with earlier editions back to mid-20th century) and is often used alongside other environmental and humidity-related standards (for example, ISO 291 and ASTM practices for alternative humidity-generation methods).

Q: What are the key keywords?

A: Relative humidity, saturated salt solution, humidity fixed point (HFP), hygrometer calibration, environmental conditioning, corrosive vapors.