Responding to an alkali spill

Purpose

To take a caustic spill off a surface without adding heat to it, without putting it into a metal it attacks, and without leaving behind the residue that later cements a cap or frosts a bottle.

When to use it

Solid sodium or potassium hydroxide; a concentrated hydroxide or carbonate stock; a spilled developer, which is alkaline; and ammonia solution, which is on this page because it is stored with the alkalis and behaves like none of them.

Before you start

You should already have read why the substance goes into the water and never the water into the substance, on storage and incompatibilities, and the sensitisation section of protecting yourself, because a spilled developer is a skin-contact event before it is a housekeeping one.

This is a Level B procedure: chemical splash goggles, an impervious apron, new gloves heavier than the working pair, and eyewash provision within reach. Nitrile holds unusually well against strong alkali — the published figure is more than 360 minutes for a 0.56 mm glove at 50 per cent sodium hydroxide — but that is a total-immersion test on a much thicker glove than the one you own, so it is a ranking rather than a permitted contact time. The glove reference carries the argument.

☠Three things that sound sensible and are not

Do not wet a solid caustic spill. Dissolving sodium hydroxide releases enough heat to make it steam and spatter, and enough to ignite combustible material beside it. Water is what turns a spill you could have lifted into a hot one you cannot.

Do not neutralise it where it lies. Bringing a dilute alkaline rinse to a workable pH is a waste operation, done slowly, in a ventilated place, in full protective equipment — not a response to a spill and never a treatment for skin. The first aid reference states the course’s position: the sources give water, at length, and no neutralising treatment.

Do not collect it in aluminium, tin or zinc. Caustic corrodes them and evolves hydrogen. The foil tray, the baking tray pressed into service as a drip tray and the saucepan used as a water bath are all in a kitchen and none of them is a vessel for this. Use plastic.

Procedure

1. Stop, set the vessel down upright, and say aloud what has spilled and how strong it was.
2. Goggles on, then new heavier gloves, then the apron.
3. Get any metal out of the way — the drip tray, the foil, the pan, the tools — before anything else moves.
4. If it is a solid, lift it dry by collecting a spilled solid and come back here at step 6. Dry lifting is not a preference on this page; it is the whole difference.
5. If it is a solution, absorb from the edge inwards with granules or a mat, then lift the loaded absorbent into a tub and close it.
6. Take up the residue with a damp disposable wipe, and then wipe again with a fresh damp one. A caustic residue you cannot see is what carbonates, cements the next cap shut and frosts the next glass bottle that stands on it.
7. Wash the surface with a small volume of water and collect the rinse. Small, because every extra litre is another litre you have to store.
8. Route the rinse and the absorbent to the container for its own stream — an alkaline stream, never into the acid container, and never into a container you would then cap and forget. What may lawfully be done with it afterwards depends on where you are, and the disposal caveat is where this course stops rather than guessing.
9. Check the shelf the spill came from: a hydroxide bottle that has been open is part carbonate, and a cap with a crust on its threads will not seal again.
10. Gloves off by the removal sequence, into the bag, and hands washed — with a pH-balanced cleanser if any of it reached skin, because ordinary soap is itself alkaline.
11. Write it down.

How you know it worked

• Nothing was wetted that could have been lifted dry, and nothing warmed under your hands.
• No metal vessel, tray or tool holds any part of what you collected.
• The surface has been wiped twice and is not slick or soapy to a gloved fingertip.
• The container that received it holds one stream only.
• The bottle it came from has a clean neck and a cap that turns freely.

If a step fails

Step 3, it has already run into a foil tray or a metal pan. Get it out of the metal and into plastic, ventilate, and do not seal the plastic container tightly until you are sure nothing is still gassing. Hydrogen from a caustic attacking aluminium is combustible.

Step 4, you wetted the solid before you read this. If it steamed or spattered, treat it as an exposure first and a spill second: it has thrown hot caustic droplets further than the spill went. Come back to the bench once you have dealt with anyone it reached.

Step 6, the residue keeps coming back. It is carbonating out of the air as fast as you lift it. Two damp wipes and a rinse are enough; a third pass is a sign the bulk was never collected.

Step 8, you are tempted to tip it into the acid container to save a bottle. Do not. The acid container is the one that ends up as a general receptacle at the end of a tiring session, and it is the container that then makes a gas under its cap. One stream per container is the rule routing general chemical waste enforces.

The spill is ammonia solution. The hazard is the vapour rather than the puddle, and the room is the control: open the window, leave, and let the air change before you go back to it. Ammonia has a long-term workplace limit of 25 ppm and 35 ppm over fifteen minutes. Carry nothing from it towards the silver nitrate shelf — that pairing is the one genuinely explosive possibility in an ordinary photographic laboratory, and the matrix sets out why.

Any of it reaches skin or an eye. Stop the clean-up and irrigate, at length, and keep going past the point where it feels better. A chemical burn is an emergency-department injury.

What to record

The substance, its strength and its form, the volume, and what metal was in the room. Then what you lifted, what you absorbed, which container received it, and whether the source bottle’s cap and neck were sound. If the spill came from a bottle whose stopper had cemented, that belongs in the entry too: it is the failure that caused the spill rather than the spill itself.