"Store at controlled room temperature" appears on bacteriostatic water and on a large share of laboratory materials. It is a defined term with a specific meaning, an excursion allowance, and a monitoring expectation, and it is looser than many laboratories assume and stricter than a few.
The definition
The pharmacopeial definition of controlled room temperature (CRT) is a temperature maintained thermostatically that encompasses the usual working environment of 20 to 25 °C (68 to 77 °F), with excursions between 15 and 30 °C (59 and 86 °F) permitted provided the mean kinetic temperature does not exceed 25 °C. Transient spikes up to 40 °C are tolerated if they last no more than 24 hours, and the label may state that the product should be stored at 25 °C with excursions to 15 to 30 °C, which is the wording most labels use.
Mean kinetic temperature
Mean kinetic temperature (MKT) is not a simple average. It is a single calculated temperature that would produce the same total degradation as the actual fluctuating temperatures did, and because degradation rates rise exponentially with temperature, MKT weights warm periods more heavily than cool ones. A storage area that spends half its time at 20 °C and half at 30 °C has an arithmetic mean of 25 °C but an MKT above 25 °C. The practical consequence: an area that runs warm for part of the year is more of a problem than its average suggests, and an area that runs cool is less of one.
What this means for bacteriostatic water
- Target 20 to 25 °C. An ordinary conditioned room qualifies. A basement stockroom, an unconditioned outbuilding or a loading dock often does not.
- Brief excursions to 15 to 30 °C are fine. Shipping, a warm afternoon, a cool night.
- Freezing is never permitted. The excursion allowance stops at 15 °C for a reason, and below 0 °C the product is physically damaged. See temperature excursions.
- Refrigeration is outside CRT but harmless to this product; it is unnecessary rather than damaging. See refrigeration guidance.
- Sustained heat above 30 °C pushes MKT over the limit and accelerates preservative oxidation. See benzyl alcohol oxidation.
Monitoring a storage area
- Place a min/max thermometer or, better, a logging sensor at the storage location itself, at the height of the product, not at the thermostat on the far wall.
- Record weekly at minimum; a logger records continuously and lets MKT be calculated.
- Set alert thresholds at 15 and 30 °C, and investigate any reading outside them: how long, and what was on the shelf.
- Review the record quarterly and when seasons change; many storage problems are seasonal.
- Keep the records with the inventory log. See lot traceability.
Common CRT failures
- Storage beside an autoclave, oven, incubator or radiator.
- A window shelf in direct sun.
- An unheated stockroom in winter that dips below freezing overnight.
- A refrigerator used "to be safe" that runs cold enough to freeze at the back.
- A delivery left in a vehicle or at a dock over a weekend.
Why it is written this way
The expiration date on a vial is supported by stability studies run at 25 °C (long-term) and 40 °C (accelerated); see how expiration dates are set. CRT is the storage condition under which those data apply. Stay inside it and the printed date means what it says; leave it and the date no longer describes the product. The full storage practice is in how to store bacteriostatic water.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.