Physical State

Detailed Description

The physical state of a substance refers to its form at ambient temperature and pressure (typically 20°C and 101.3 kPa). It is one of the most fundamental physical properties reported in a Safety Data Sheet and is essential for proper handling, storage, and risk assessment.

Physical states are generally classified into three main categories:

Solid: A state of matter characterized by structural rigidity and resistance to changes of shape or volume. Solids can be crystalline, amorphous, or polymeric.
Liquid: A state of matter that flows freely but maintains a constant volume, regardless of the shape of its container. Liquids can be further characterized as viscous, non-viscous, or colloidal.
Gas: A state of matter that has no fixed shape or volume and expands freely to fill any container. Gases are highly compressible and can be liquefied under pressure or cooling.

Additional classifications sometimes used include:

Semi-solid: Materials that exhibit properties of both solids and liquids (e.g., gels, pastes, creams).
Plasma: An ionized gas consisting of positive ions and free electrons. Not commonly encountered in standard chemical safety assessments.

Importance in Safety Data Sheets

The physical state of a substance significantly influences:

Exposure routes: Gases and fine powders present inhalation hazards, while liquids may pose splash hazards.
Storage requirements: Different physical states require different containment strategies.
Handling procedures: Appropriate PPE and handling techniques vary based on physical state.
Emergency response: Spill control measures differ for solids versus liquids.
Transportation regulations: Classification and packaging requirements often depend on physical state.

Common Descriptors in SDSs

Physical State	Common Descriptors
Solid	Crystalline, powder, granular, flakes, pellets, beads, amorphous, fibrous, monolithic
Liquid	Viscous, non-viscous, solution, suspension, emulsion, clear, cloudy, oily
Gas	Compressed, liquefied, refrigerated, dissolved
Semi-solid	Gel, paste, cream, wax, resin

Temperature Dependence

The physical state of a substance can change with temperature. For example, water is a solid (ice) below 0°C, a liquid between 0°C and 100°C, and a gas (steam) above 100°C at standard pressure. When reporting physical state in an SDS, it is important to specify the reference temperature, typically 20°C or 25°C.

Regulatory Requirements

According to GHS and various regional regulations (EU CLP, US OSHA HazCom, etc.), the physical state must be clearly indicated in Section 9 of the Safety Data Sheet. This information is considered mandatory and must be provided for all substances and mixtures.

Best Practices

When describing the physical state in an SDS:

Be specific and descriptive (e.g., "fine white crystalline powder" rather than just "solid")
Include relevant qualifiers such as color, clarity, and texture
Specify the reference temperature and pressure if different from ambient conditions
For substances that can exist in multiple states under normal conditions, provide information about phase transitions
Ensure consistency with other physical properties reported in the SDS