Mixing Cleaners and the Gases They Make

Why this matters

Most toxic-gas exposures in residential service work are not dramatic leaks. They are two ordinary products meeting in a toilet bowl, a sprayer tank, a shower pan or a drain, usually because one person used the first product and a second person, or the same person an hour later, used the second. The products are each safe on their labels. Together they make chlorine, chloramine, or enough heat to boil a drain line back into someone's face. Cleaning techs, pool techs, plumbers, pressure-washing crews and appliance techs meet these pairs every week.

Acid and caustic handling as such, including hydrofluoric acid in coil cleaners, is owned elsewhere: see related: Acid + Caustic Chemical Handling Reference. Opening a drain that may already hold an opener has its own procedure: see related: How to Open a Drain That May Hold Chemical Opener. This card is the map of which pairs react, what they make, and which trade meets each.

The reactions worth knowing by heart

Bleach and ammonia: the cleaning trade's version

Household bleach is a solution of sodium hypochlorite. Mixed with ammonia, it forms chloramines, a family of irritant gases. The classic exposure is not a person deliberately mixing two bottles; it is a mildew spray with bleach used on a shower, followed by a glass cleaner with ammonia on the shower door, in a closed bathroom. Or bleach poured into a toilet or litter area where urine, which releases ammonia as it breaks down, is already present.

Chloramine exposure ranges from a cough that clears in fresh air to lung injury needing hospital care, depending on concentration and time. The cue is a sharp, chlorine-like, choking smell that appears when the second product goes on. Stop, leave the room and ventilate from the doorway.

Bleach and acids: the one that makes chlorine

An acid releases chlorine gas from hypochlorite. The acids involved are everywhere on a service truck: hydrochloric acid in many toilet bowl cleaners and in muriatic acid, phosphoric and sulfamic acids in descalers and rust removers, citric and acetic acids (vinegar), oxalic acid in wood brighteners.

Chlorine is heavier than air and a severe respiratory irritant. OSHA's limit is a ceiling of 1 ppm (29 CFR 1910.1000, Table Z-1); NIOSH recommends a 15-minute ceiling of 0.5 ppm and lists 10 ppm as immediately dangerous to life or health. Smell is not a measure. You can smell chlorine at well below its limit, which makes the early warning reliable, but the sense of smell dulls with exposure, so a room that "stopped smelling" while you stayed in it may be no better. The all-clear is time in fresh air and a ventilated room, never a nose.

Where it happens:

• Cleaning: a bowl cleaner squirted into a toilet that was bleached an hour before; a descaler on a shower head over a bleached tub.
• Pressure washing: a soft-wash mix of sodium hypochlorite run through a pump, tank or hose that next carries an acid brightener for wood or a rust remover, without a full rinse between.
• Pool: muriatic acid poured near or onto a chlorine product, or acid and chlorine stored on the same shelf where the fumes from a loose acid cap meet a torn chlorine bag.
• Plumbing and appliance: a descaler run through a washer or dishwasher that was just cleaned with bleach; an acid opener poured into a drain someone had already bleached.

Pool chemicals: two chlorines that must never meet

Pool techs carry the most dangerous pair on this card. Calcium hypochlorite (cal-hypo, granular or tablet shock) and trichloroisocyanuric acid (trichlor, the common slow-dissolving tablet) are both chlorine sources, and they react violently with each other, producing heat, fire, an explosion in a closed container, and chlorine gas. Trace amounts are enough: cal-hypo dropped into a feeder or a bucket that held trichlor has caused explosions.

Cal-hypo is also a strong oxidizer. Contaminated with oil, grease, brake fluid, sawdust, a little soda or other organic material, it can heat and ignite. Mixed with a small amount of water (as opposed to dissolved into a lot of water) it can heat sharply.

Rules the pool trade lives by, all of them about separation:

• Each chemical gets its own scoop, bucket and feeder, labeled, never shared.
• Add chemical to water, never water to chemical, and pre-dissolve cal-hypo in a bucket of pool water rather than wetting the granules.
• Store cal-hypo, trichlor and acid apart, in their original containers, with acid on a shelf below oxidizers so a drip cannot reach them, and nothing organic on the same shelf.
• Never pour two products into the skimmer, feeder or the same spot in the pool at once. Let one disperse first.

Drain openers in standing water

Drain openers are either strongly alkaline (sodium hydroxide or potassium hydroxide, sometimes with bleach) or strongly acidic (concentrated sulfuric acid). A caustic opener and an acid opener in the same trap neutralize each other violently, and the heat can boil the water in the trap and throw it out of the fixture, carrying both chemicals with it. A bleach-containing opener meeting an acid opener also releases chlorine.

The trap that does not drain is the one most likely to hold a homeowner's opener, because they tried it first. Ask before you plunge, snake or pour anything, and treat standing water in a slow drain as chemical until shown otherwise. See related: How to Open a Drain That May Hold Chemical Opener, which owns the method, and Acid + Caustic Chemical Handling Reference for eye and skin protection.

A worked bathroom: how much chlorine one mistake makes

A cleaning tech bleaches a toilet bowl with about 50 milliliters of a 6 percent household bleach, then a teammate adds an acid bowl cleaner in excess. The bathroom is 5 by 8 feet with an 8-foot ceiling, 320 cubic feet or about 9.06 cubic meters, door closed, fan off.

Work out the worst case, where all the hypochlorite reacts and the gas spreads evenly through the room:

• 50 milliliters at 6 grams per 100 milliliters is 3 grams of sodium hypochlorite.
• 3 grams divided by about 74.4 grams per mole is about 0.040 moles, which can release up to about 0.040 moles of chlorine.
• 0.040 moles times about 70.9 grams per mole is about 2.86 grams, or 2,860 milligrams, of chlorine.
• 2,860 milligrams spread through 9.06 cubic meters is about 316 milligrams per cubic meter.
• Converting at room conditions (multiply by 24.45, divide by the molar mass of 70.9) gives about 109 ppm.

That is an upper bound: not all of the hypochlorite reacts at once, some chlorine stays dissolved in the bowl water, and the gas is concentrated near the bowl before it spreads. But even if only a tenth of it reached the room air, about 11 ppm would be above the 10 ppm NIOSH treats as immediately dangerous, and over twenty times the 0.5 ppm NIOSH ceiling. Near the bowl, where the tech is bent over with a brush, it is higher.

What changes the answer. A flush between the two products takes most of the bleach down the drain before the acid arrives, which is why "flush, wait, then the next product" is the rule. A running exhaust fan cuts the concentration that builds in the room but not what the tech breathes at the bowl in the first seconds. A bigger room dilutes the same chlorine further; a half bathroom of half the volume doubles it.

The never-mix list and the van

Never mix, in a container, a sprayer, a pump, a drain or on a surface:

• Bleach with ammonia, with any acid (including vinegar), or with rubbing alcohol.
• Calcium hypochlorite with trichlor, with acid, with anything organic, or with a small amount of water.
• Acid drain openers with caustic drain openers, or either with bleach.
• Two different chlorine products, ever.
• Hydrogen peroxide with vinegar.

On the van and in the bucket:

• Store oxidizers (bleach, cal-hypo, trichlor) and acids on separate shelves or in separate bins, acids low, with nothing organic beside the oxidizers.
• One product per sprayer and per tank, labeled with the contents as the secondary container labeling rules require; see related: HazCom - Secondary Container Labeling Protocol. A sprayer is never "rinsed out" from bleach to acid; it is a different sprayer.
• Flush or rinse a surface, a bowl or a drain between products, and wait a few minutes with the room ventilated.
• Read section 10 of the safety data sheet, stability and reactivity, which lists incompatible materials, for any product you are about to use after another.

If a mix happens

• Leave the area immediately and take everyone with you, including the customer. Close the door behind you if it is on your way out.
• Ventilate from outside: open an exterior window or door from outside the room if you can, run an exhaust fan only if its switch is outside the room. Do not go back in to clean up or to "neutralize" the mix with another product.
• Get anyone exposed into fresh air. Call 911 for trouble breathing, chest tightness that does not settle, confusion or collapse. Poison Control (1-800-222-1222 in the U.S.) advises on lesser exposures and on what was mixed.
• Eyes: flush with clean, lukewarm water for at least 15 minutes and get medical care, following mainstream first aid guidance (American Red Cross).
• Re-entry waits until the room has been ventilated well and the smell has gone in fresh air from outside. Report what happened, with the products and quantities, because the person treating someone asks for exactly that.

References

• 29 CFR 1910.1000, Table Z-1, chlorine ceiling and ammonia limits; 29 CFR 1910.1200, Hazard Communication, including safety data sheet section 10 and secondary container labeling
• NIOSH Pocket Guide to Chemical Hazards, chlorine and ammonia (RELs and IDLH values)
• CDC and U.S. Consumer Product Safety Commission guidance on pool chemical storage and handling
• See related: Acid + Caustic Chemical Handling Reference; How to Open a Drain That May Hold Chemical Opener; HazCom - Secondary Container Labeling Protocol; HazCom + SDS (Chemical Right-to-Know)