Storage near radiators: caking sachets in summer wards

Thirty-one degrees at four in the afternoon, measured on a thermometer that the ward had bought for the fridge and then stopped using. The store room is 2 metres by 3, has a south-facing window with no blind, and a heating pipe running along the wall at ankle height. Three cartons of sachets were stacked against that wall from May until August.

By the end of July, every sachet in the bottom carton felt like a small bean bag. Squeeze one and the powder inside had set into a soft brick that had to be broken up with a spoon handle before it would pour. That is caking, and it does not announce itself until someone is standing over a container at two in the morning.

What happens to the powder

Superabsorbent polymer is designed to pull water out of the air as well as out of urine. The foil laminate on a sachet is a good barrier while it is intact, but it is a barrier against a gradient, not an absolute seal. Sit a carton in a warm room with a relative humidity above 65% for three months and the powder will take up moisture through the seams, the pinholes and any fold that has been flexed a hundred times in handling.

What you get is not a failed product. It is a product that has partially pre-absorbed, which means it now has less capacity left for the job, and it has become a solid block that doses unevenly.

Three places that fail in summer

The first is the radiator shelf, which is where the sachets go because it is at chest height and out of the way. The second is the windowsill, which is worse, because it adds ultraviolet light to the heat. The third is the top of a cupboard in a sluice room, where the ambient humidity sits near saturation for most of the day.

A community hospital we visited had all three in one building. The pharmacy store was fine, cool and dark. The ward stocks were not, and the wards that ran out and borrowed from pharmacy were the ones with the fewest dosing problems. Nobody had made the connection between caked powder and soft sets, because a caked sachet still pours if you squeeze it hard enough, and the dose that comes out is a guess.

Where it should go instead

Below 25 degrees, below 60% relative humidity, off the floor, out of sunlight, and at least a metre from any heating pipe. In practice that means a closed cupboard in an internal room, not a shelf above a radiator.

• Keep cartons closed. An open carton in a humid room is a slow sponge.
• Rotate stock so the oldest carton is used first, and write the delivery date on the end.
• Never store sachets in a room that also houses a washer or a sluice sink without extraction.
• Keep a thermometer and humidity card in the store and read them weekly, not annually.

If a store room regularly exceeds 25 degrees in summer, a portable dehumidifier costs less than one written-off carton and does the job in a room that size.

The squeeze test

You do not need a lab. Take one sachet from each carton at the start of each month and squeeze it between finger and thumb. It should feel like a bag of fine sand, with movement inside. If it feels like a single soft block, the batch has taken up moisture and should be quarantined, not used.

Then cut it open and pour it into a jug of 500 ml of water. A healthy sachet will gel the lot in under a minute. A caked one will float in lumps, gel slowly and leave clear liquid at the bottom. That test takes two minutes and settles the argument about whether the powder is at fault.

When sets start failing across a building rather than in one room, storage is the second thing to check after scoop weight, and it is the thing nobody thinks of. Ask where the stock has been since delivery, not where it is now. The answer is often a corridor, a cupboard above a boiler or the boot of a care manager’s car.

A hospice in the south west traced three months of intermittent soft sets to a stock rotation error: a new delivery was put in front of the old one, the old carton sat at the back of a warm cupboard through the summer, and it was opened in October. The powder was nineteen months old and had spent four of those months at 29 degrees.

The SAP powder specifications list the storage conditions and shelf life for each grade, and they are worth taping inside the store door where the person receiving a delivery will see them.

Go and stand in your store room at three in the afternoon this week. If it is warmer than the corridor, move the stock, and put a thermometer on the shelf so the next person can see what you saw.