Pool and Cleaning Chemical Incompatibility in Storage

Why this matters

Most chemical injuries in this trade do not happen while someone is using a product. They happen on a shelf, in a van tub or in a garage, when two products that were each stored correctly are stored next to each other. A jug of acid drips onto a bucket of chlorine granules, a cracked lid lets humid air into a pail of oxidizer sitting beside the mower fuel, and the first anyone knows of it is a cloud of gas or a fire that firefighters treat as a hazmat call. The fix costs a second tub and ten feet of wall. The skill is knowing which pairs matter before you load the shelf.

Four pairs that cause almost all of it

Sort every product you carry into one of six families by reading its label and Section 10 of its safety data sheet (stability and reactivity): hypochlorite oxidizers, stabilized chlorine, acids, bases (caustics), ammonia products and fuels and organics. Then learn these four pairs, because they account for the events that actually happen in shops and vans.

Hypochlorite plus acid releases chlorine gas. Hypochlorite is the active chemistry in liquid chlorine (sodium hypochlorite, sold to pool techs at roughly 10 to 12.5 percent strength), household bleach (much weaker, but the same reaction) and cal hypo (calcium hypochlorite granules or tablets). Acids in a service van include muriatic acid (hydrochloric), dry pH reducer (sodium bisulfate), sulfuric drain openers and many descalers and rust removers. A small leak of acid into a bleach puddle gives off chlorine in seconds. It is heavier than air, so it pools in a van floor, a basement or a garage with the door down.

Hypochlorite plus ammonia releases chloramine gas. Ammonia lives in glass cleaners, some all-purpose cleaners, some floor strippers and in urine-contaminated waste. This is the pair that injures cleaning crews mixing in a mop bucket, and in storage it shows up when a cleaning cart carries a bleach jug and an ammonia spray bottle in the same caddy and one leaks into the other.

Cal hypo plus stabilized chlorine can ignite or explode. This is the one that surprises pool techs, because both products say chlorine. Stabilized chlorine is trichlor (trichloroisocyanuric acid, the slow tablets) and dichlor (the granular shock). Mixed with cal hypo, even as dust in a shared scoop or bucket, they react violently and can burn. Never share a scoop, a feeder, a bucket or a shelf between them.

Oxidizers plus fuels and organics start fires. Cal hypo, dichlor, trichlor and peroxide-based oxygen bleaches are oxidizers: they supply oxygen to a fire, which means a small ignition becomes a fast, hot one that ordinary suppression struggles with. The fuels they meet in a shop are gasoline, two-stroke mix, motor oil, brake fluid, antifreeze, solvent, paint thinner, oily rags, cardboard, wooden pallets and fertilizer. Cal hypo contaminated with a few drops of oil or brake fluid has ignited on its own.

One more pair is worth a line. Acid plus base (an acid drain opener poured where a caustic one already sits, or two jugs leaking into one tub) produces violent heat and spattering rather than gas.

Why the label's storage line is not enough

Every label says something like "store in a cool, dry, well-ventilated place away from incompatible materials." That sentence is accurate and useless on its own, because it does not tell you what the incompatible materials are or how far away is away. Section 10 of the SDS, a section OSHA's Hazard Communication Standard requires on every sheet, names the incompatibles by family; Section 7 (handling and storage) gives any specific conditions. Read both for every product on the shelf, then build the layout from the families rather than from the products. Segregate by product name and trichlor ends up beside cal hypo because both are filed under "pool."

See related: Reading a Safety Data Sheet: The Sections That Matter.

The garage fire pattern

When a pool or cleaning storage area burns, the sequence is nearly always the same, and every link is a storage choice:

1. An oxidizer pail with a lid that no longer seals. Cal hypo is hygroscopic, meaning it pulls moisture from the air. A small amount of water on cal hypo produces heat rather than dissolving it safely. Summer humidity in a closed garage is enough to start that on a damaged pail.
2. Something above it that can drip. A jug of acid, a case of liquid chlorine, a bottle of brake fluid or an oil can on the shelf over the granules. Liquids stored above solids is the single most common layout error.
3. A fuel within reach. The mower, the gas can, a stack of cardboard boxes from the last delivery.
4. No one there. These fires start overnight or on a weekend, in a building with the door shut, and by the time anyone notices, the oxidizer is feeding the fire and the hypochlorite is giving off gas.

Break any one link and the event does not happen. Layout can break the first three; nothing in a layout breaks the fourth, which is why the first three all have to go rather than whichever one is easiest.

Layout rules that break the chain

These are shop defaults that hold for the quantities a small residential shop keeps. Your fire marshal applies the adopted fire code (the International Fire Code or NFPA 1, which point to NFPA 400 for oxidizers, in whatever edition your jurisdiction has adopted) and that governs if it says more.

• Separate by family, with a barrier or a distance. A solid wall, separate cabinets or separate secondary-containment tubs. A shop default is that no two incompatible families share a shelf unit, and oxidizers sit at least 20 ft from fuels or behind a wall from them.
• Liquids below solids, always. Nothing that can leak sits above an oxidizer solid. If a liquid must sit on the same unit, it goes on the bottom shelf, in a tub.
• Every liquid in a tub sized to hold the largest container in it. A tub that holds one gallon under four one-gallon jugs contains a single failure and nothing more. Size it to the biggest container plus a margin.
• Stabilized chlorine and cal hypo never share anything. Separate shelf units, separate scoops labeled by product, separate buckets for mixing.
• Keep oxidizers dry and closed. Lids tight, off the floor, out of direct sun, never in a room that floods or sweats. A damaged pail gets its contents moved to a sound, labeled container the same day, wearing splash goggles, chemical gloves and a respirator under a written program per 29 CFR 1910.134 if the SDS calls for one for the dust.
• No cardboard or pallets under oxidizers. Steel or plastic shelving only. Sweep up spilled granules with a dedicated clean dustpan, never with a broom that has swept oily floors.

The van is the same problem at closer range

A van compresses the shop into a few cubic feet and adds heat, vibration and braking. The same families apply, with three additions. Acids and hypochlorites ride on opposite sides of the van in separate tubs, so a jug that splits under braking cannot reach the other. Fuel cans ride in a vented exterior box or a dedicated locker, never in the cargo area with oxidizers. Nothing chemical rides in the cab, where a leak puts gas at the driver's face. How much you may carry and how it must be marked is a transport question owned elsewhere.

See related: Hazardous Materials in the Service Van; Loading the Van So Chemicals, Cylinders and Batteries Ride Safely.

Worked example: one pool shop's storage wall

A three-van pool shop asked for a storage check after a near miss: a tech had opened the shop on a Monday to a strong chlorine smell. The walk found this on one shelf unit and the floor beside it:

• Top shelf: two 50-lb pails of cal hypo shock, one with a cracked lid; a 50-lb pail of trichlor tablets beside them.
• Middle shelf: four 1-gallon jugs of muriatic acid, loose, no tub.
• Bottom shelf: two 4-gallon cases of liquid chlorine.
• Floor, about 3 ft away: the shop's push mower and a 5-gallon gas can.
• On the cleaning cart by the door: a gallon of bleach and a spray bottle of ammonia glass cleaner in the same caddy.

The smell had a likely source: one acid jug had a weeping cap, and its drips had run down onto the liquid chlorine cases below. Before anyone sorted anything, the shop was ventilated with both bay doors open for half an hour and nobody went back in on the strength of the smell fading, because chlorine dulls the sense of smell at concentrations that still injure. Re-entry waited for the full half hour and for the weeping jug to be capped and carried out, wearing splash goggles and acid-resistant gloves.

The walk counted five conflicts:

1. Cal hypo beside trichlor on the top shelf (the explosion pair).
2. Acid stored directly above liquid chlorine (the gas pair, already happening).
3. Oxidizers about 3 ft from a gas can and a fueled mower (the fire pair), well inside the 20 ft default.
4. A cracked cal hypo lid in a garage that reaches high humidity in summer (the self-heating link).
5. Bleach and ammonia cleaner in one caddy (the chloramine pair).

The fix took one afternoon and nothing exotic. The trichlor moved to its own shelf unit on the opposite wall with its own labeled scoop. Cal hypo stayed on the original unit, with the cracked-lid pail decanted into a sound labeled pail outdoors, wearing splash goggles, chemical gloves and the respirator the SDS names for the dust, under the shop's 1910.134 program. Liquid chlorine moved to the bottom shelf of the cal hypo unit in a tub, since both are hypochlorites and compatible with each other. The acid went into a tub on a third unit, on the bottom shelf, about 25 ft from the hypochlorites. The mower and gas can moved outside to a shed. The ammonia glass cleaner came off the cart and was replaced with a non-ammonia product, so the cart now carries one oxidizer and no ammonia. Five conflicts found, five closed, and the three links of the garage fire chain that a layout can reach (the bad lid, the liquid above, the nearby fuel) are each broken.

WALL 1 (pool oxidizers)     WALL 2          WALL 3
+-------------------+   +-------------+  +-------------+
| cal hypo pails    |   | trichlor    |  | (empty)     |
| dry, lids tight   |   | own scoop   |  |             |
+-------------------+   +-------------+  +-------------+
| (empty, no liquid |   | (empty)     |  | (empty)     |
|  above solids)    |   |             |  |             |
+-------------------+   +-------------+  +-------------+
| liquid chlorine   |   | (empty)     |  | acids, tub  |
| in a tub          |   |             |  | 25 ft away  |
+-------------------+   +-------------+  +-------------+
 fuel and mower: outside shed, not in the building

What changes the answer

Quantity. A shop that keeps pallets of cal hypo, not a few pails, has crossed into the territory the fire code regulates by maximum allowable quantity per control area, and may need rated storage, sprinklers or a permit. That threshold depends on the oxidizer class in the SDS and on your local adopted code, so it is a question for the fire marshal, not this card.

Rented or shared space. If your storage is in a leased unit beside other tenants, your neighbor's solvents count. Ask the landlord what is stored on the other side of your wall.

How to check you got it right

Walk the storage with the SDS for each product in hand and, for every shelf, name what is above, below and beside each oxidizer and each acid. If the answer to any of those is an incompatible family, or a liquid above a solid, it is not done. Then repeat the check every time a new product comes into the shop, because the layout is only as good as the last delivery.

References

• OSHA Hazard Communication Standard, 29 CFR 1910.1200 (Section 7 and Section 10 content of the SDS)
• NFPA 400, Hazardous Materials Code, in the edition your jurisdiction's fire code adopts, for oxidizer storage
• CDC guidance on preventing pool chemical injuries
• See related: Hazardous Materials in the Service Van; Reading a Safety Data Sheet: The Sections That Matter; The Chemical Spill Response SOP for a Service Van