The sensitivity solution is dilute and confirms the wearer can detect the agent; the test solution is concentrated and is used during the test.

They are used at different stages and are not interchangeable.

Using the test solution for sensitivity would pass everybody.

Using the sensitivity solution for the test would fail everybody.

Confusing them is a real error rather than a theoretical one.

Separate nebulisers are used for each to prevent cross-contamination.

They have a shelf life and a shorter working life once opened, and both matter.

Solutions degrade over time, accelerated by temperature and light.

An out-of-date solution may no longer be detectable at the intended concentration.

Solutions decanted into nebulisers should be replaced regularly rather than topped up.

Contamination from repeated use also affects them.

Dates should be checked before a testing session rather than discovered afterwards.

They block with crystallised solution and wear, delivering less agent than the method assumes.

Correct droplet size and delivery rate are part of the method.

A blocked or worn nebuliser produces false passes.

Rinsing after use prevents most blockages.

Separate nebulisers for sensitivity and test solutions prevent cross-contamination.

Checking output before a session takes a moment and prevents a day of invalid tests.

Because every one of them reduces the amount of agent reaching the wearer.

A degraded solution, a blocked nebuliser and a short test all deliver less challenge.

Less challenge means less chance the wearer detects anything.

So the failure mode is a quiet false pass rather than a false failure someone would investigate.

That is what makes consumable management consequential rather than administrative.

It also means a testing programme can look successful while certifying people whose respirators do not fit.

In practice yes - they scratch, cloud and tear with use.

A clouded hood makes the exercises harder to conduct and observe.

Tears let the challenge agent escape, reducing the concentration inside.

That is another route to a false pass.

Hoods are inexpensive relative to the value of a valid test.

Replacing them on condition rather than on a schedule is usually sufficient.

They should not be - concentrations and formulations differ between suppliers and methods.

The method assumes a specific agent at a specific concentration.

Substituting another product changes what the test demonstrates.

Kits are supplied as matched sets for that reason.

Topping up one supplier's solution with another's makes the concentration unknown.

Using the kit manufacturer's own consumables keeps the method as it was validated.

Batch and expiry details alongside the test records, so a suspect result can be traced back.

If a solution is later found to be out of date, the affected tests can be identified.

Without that link, the only safe response is retesting everyone.

Nebuliser cleaning and replacement are worth logging for the same reason.

It costs almost nothing during the session and saves considerable work later.

How long to keep the records is a jurisdictional question rather than a housekeeping one.