Responding to an acid spill

Purpose

To get an acid off a surface before it reaches anything that will give up a gas to it, and to do that in the right order — the containers move first, the absorbent second.

When to use it

Any acid outside its vessel: a working stop bath, a citric or acetic concentrate, the acid rinse off a graduate, or the contents of the acid waste container. The volume is not what makes this urgent. What makes it urgent is that a darkroom’s shelves are full of the salts of weak acids, and a spill travels.

Before you start

You should already have read the pattern behind two-thirds of the incompatibility matrix — an acid liberates a volatile weak acid from its salt — and know where your own sulfite, thiosulfate, ferricyanide and waste containers stand, from storage and incompatibilities.

This is a Level B procedure: chemical splash goggles, new gloves heavier than the ones you work in, an impervious apron, eyewash provision within reach, and the spill kit at the wet bench rather than in another room.

☠What an acid must not be allowed to reach, and what each meeting makes

Sulfite, bisulfite and metabisulfite give sulfur dioxide. Thiosulfate gives sulfur dioxide and a milky cloud of sulfur, and it is the most likely of these accidents in a home darkroom because the two liquids are adjacent in the tray sequence and adjacent again in the waste corner. Sulfide gives hydrogen sulfide; ferricyanide with hot acid can give hydrogen cyanide; household hypochlorite gives chlorine. Every one of those is worse inside a capped waste bottle than on an open bench, because the gas waits under a cap you will later unscrew. The matrix carries the equations and the exposure limits; this page carries the steps.

Procedure

1. Stop, set the vessel down upright, and say aloud what has spilled and at what strength.
2. Look where it is running, not at where it landed.
3. Move or cover what is in its path, before you touch the spill itself — the fixer tray, the sulfite jar, the waste containers, the ferricyanide. Caps on, lids on, and lift them clear rather than sliding them through the puddle.
4. Decide whether this is yours to clean at all. A concentrate, a spill you cannot reach the edge of, a smell that makes you want to leave, an outlet or an appliance in the way, or any hesitation, and you leave: out, door closed, ventilated from outside, advice sought with the product name and its sheet in your hand.
5. If you are staying: goggles, then new heavier gloves, then the apron.
6. Absorb from the edge inwards with granules or a mat, so the spill stops travelling. Never a dry cloth, which pushes it outwards and loads the cloth.
7. Lift the loaded absorbent into a bag or tub and close it.
8. Take up the residue with one damp disposable wipe.
9. Wash the surface with a small volume of water, and collect the rinse. Never add water to a spilled concentrate to dilute it in place; the heat and the spatter are the reason the rule runs the other way at the bench.
10. Route the rinse and the loaded absorbent to the acid stream, in its own container, and nowhere near the fixer or the developer containers. What may then lawfully be done with that container is a local question, and the disposal caveat is where the course stops.
11. Check the drain if any of it reached the sink. Kodak’s rule is to run plenty of water before and after, and never into a trap where a chlorine-bearing cleaner is standing.
12. Gloves off by the removal sequence, into the bag, hands washed.
13. Write it down, and check the pH of any solution the acid may have splashed into before you use it again.

How you know it worked

• Nothing that could have met the acid is still in the place it was when the spill started.
• No container has gained a stream that is not its own, and the acid container has gained nothing but acid.
• The surface is dry, including the bench lip and under the trays, and the rinse was collected.
• Nobody smelled anything sharp after the clean-up, and nobody is still wearing the gloves that were on when it happened.
• The notebook entry names the strength as well as the volume.

If a step fails

Step 3, it has already reached the fixer, the sulfite or the waste container. Leave. This is the sulfur dioxide case, and it is one of the leave-the-room criteria rather than a clean-up. Close the door, ventilate from outside, and do not unscrew a waste container that may have made a gas under its cap.

Step 3, it has reached a sulfide or a ferricyanide. The same answer, sooner. Hydrogen sulfide and hydrogen cyanide are not spills you work through, and both have limits an order of magnitude below the point at which a room feels wrong.

Step 4, you cannot decide. Leave. Twenty minutes out of the room costs a session; the other error does not cost a session.

Step 6, it has reached the floor. Contain the outer edge first, then work inwards, then look at your shoes. The second contamination event is usually a footprint.

Step 9, the surface is porous. Washing lifts what is on it, not what soaked in. Collect the rinse, then record the surface as contaminated and cover or seal it before the next session.

Step 11, the sink held a household bleach. That is the chlorine pair, in the one place you cannot ventilate. Leave the room, and flush the drain only once the air has changed.

Any of it reaches you. Stop and treat the exposure — an acid burn is an emergency-department injury rather than a home one, and the first aid quick reference is the page to have read before today. The spill waits.

What to record

The acid and its strength, the volume, where it went and what stood in its path. Then what you moved first, what you collected, into which container, and whether any solution on the bench was splashed and has had its pH checked since. The sentence worth writing last is which container you had to move in a hurry, because that is a shelf problem rather than a spill problem.