Industrial hygienists and EHS consultants are often asked to evaluate the storage and transportation risks of concentrated sodium chlorite solutions. On paper, this sounds straightforward: determine vapour pressure, confirm compliance, document the result.
In practice, vapour pressure data for sodium chlorite solutions can be difficult to interpret, especially when real storage conditions do not match ideal laboratory assumptions. When pressure behaviour is questioned by regulators, clients, or carriers, the consultant is usually the one expected to explain the discrepancy.
This is where early technical discussion matters.
Why Vapour Pressure for Sodium Chlorite Is Not Always a Single Number
Sodium chlorite solutions do not behave like inert liquids with stable equilibrium vapour pressure. The measured pressure depends strongly on system configuration and chemistry, not just temperature.
Open Systems (Atmospheric Pressure)
In open tanks or vessels vented to atmosphere, the system reaches a relatively stable condition. Under these conditions, saturated vapour pressure can be measured reproducibly using standard methodologies. This value is typically what is reported and referenced in SDS documentation.
For consultants assessing open or continuously vented systems, this measurement is usually appropriate and defensible.
Closed or Semi-Closed Systems
In sealed containers, intermediate bulk containers (IBCs), or inadequately vented storage, additional processes may affect pressure over time:
- Slow decomposition reactions, producing chlorine or chlorine oxides in the vapour phase
- Interactions with container materials, particularly metals or incompatible linings, which may introduce additional gases
- Time-dependent pressure increase, rather than a true equilibrium vapour pressure
Under these conditions, internal pressure may gradually rise above atmospheric pressure even when temperature remains constant. This behaviour is often misunderstood or misattributed to vapour pressure alone, creating interpretation challenges during audits or incident investigations.
What We Can Measure — and What the Data Represents
LCS Laboratory can measure the saturated vapour pressure of sodium chlorite solutions under defined, controlled conditions. The resulting data represents vapour behaviour at equilibrium in an open or properly vented system.
It is important to distinguish this from:
- Total pressure buildup in sealed containers
- Pressure contributions from decomposition gases
- Long-term storage effects unrelated to equilibrium vapour pressure
We are explicit about these distinctions in our technical discussions and reporting, so the data is not over-applied outside its valid scope.
When This Method Is Most Useful
This approach is most appropriate when you need to:
- Support SDS preparation or review
- Address TDG / GHS vapour pressure requirements
- Evaluate open or vented storage conditions
- Provide defensible documentation where equilibrium vapour pressure is the relevant parameter
If your concern involves sealed containers, pressure relief design, or unexplained pressure increase over time, additional evaluation beyond vapour pressure alone may be required.
Using the Laboratory as a Technical Resource
Many interpretation issues can be avoided by discussing sampling conditions, container type, concentration, and intended use of the data before testing begins. We routinely work with consultants to determine whether vapour pressure measurement is appropriate, and how the results should be framed to remain technically defensible.
If you are planning sampling, updating an SDS, or dealing with results that are difficult to explain, we encourage a technical conversation before proceeding. This helps ensure the data answers the question you are actually being asked to defend. ©
