How to Handle a Small Mercury Spill

Why this matters

A broken mercury switch is a few grams of metal that looks like nothing: a handful of silver beads on the floor. The hazard is not the beads, it is the vapor coming off them, which you cannot see or smell and which rises every time the beads get smaller or warmer. Almost every instinct a tech has for a spill (sweep it, vacuum it, wipe it, rinse it down the sink) makes the beads smaller or warmer or both. A small spill handled the way EPA describes ends in a sealed jar. The same spill handled with a shop vacuum ends with a contaminated vacuum and a house that needs an air check.

Why sweeping and vacuuming make it worse

Elemental mercury is a liquid metal that evaporates slowly at room temperature. In a closed room the air above a spill can approach saturation, which at around 68 F is on the order of 13 milligrams per cubic meter, more than a hundred times the OSHA ceiling of 0.1 mg/m3 in 29 CFR 1910.1000 Table Z-2. Real rooms leak and rarely get there, but the direction is what matters, and two things push it the wrong way.

• Surface area. How fast a spill gives off vapor depends on how much exposed surface it has. One bead split into a hundred droplets has many times the surface of the original bead. A broom, a paper towel pushed hard, and a vacuum all do the splitting.
• Heat. Vapor pressure climbs steeply with temperature. A vacuum does both jobs at once: the impeller shatters beads into a fine mist and the motor warms the airstream, then the exhaust blows that warm vapor across the room. Mercury lodges in the hose, the bag or canister and the motor, and the vacuum itself becomes a source wherever it is used next. That is why the household guidance is to never vacuum mercury, and to treat a vacuum that has already been used on it as contaminated, not cleaned.

Two other habits move the problem rather than solve it. Rinsing beads down a sink drops them into the trap, where they sit for years (plumbers find old mercury in traps under dental and lab sinks for exactly this reason). And putting contaminated clothing or rags through a washing machine contaminates the machine and sends mercury to the sewer.

See related: Dose, Route, and the Exposure You Cannot See for the vocabulary of vapor exposure; this card owns the cleanup, not the dose model.

How much counts as small

Small has a meaning here, and it is set by the device, not by how calm the room looks. EPA's household guidance is written around a spill the size of a broken fever thermometer, and its advice for anything larger is to call for help rather than clean it up yourself.

The federal reportable quantity for a mercury release under CERCLA (40 CFR 302.4) is 1 pound, which is a little over two tablespoons of liquid mercury; a release at or above it must be reported to the National Response Center, and states may set lower reporting thresholds. A thermostat is nowhere near it, which is the point: by the time a spill is reportable it is long past anything a service tech should be collecting.

Step 1: Stop, and keep feet off it

Stop the work, get people and pets out of the room without crossing the spill, and close the doors to the rest of the house. The reason: shoes are how a contained spill becomes a whole-house one, and every step on a bead splits it. Skip it and beads go into carpet in the next room, where nothing in this card can get them out.

Step 2: Take the heat away and send the air outdoors

Shut off the furnace or air handler at a switch you can reach without crossing the spill, turn off any space heater, and open the windows and exterior doors in that room. Then wait at least 15 minutes outside the room before collecting, which is the interval EPA's guidance uses. The reason: forced air carries vapor through the duct system, and heat speeds evaporation. Skip it and you do the collecting in the most concentrated air the spill will ever produce.

Step 3: Size it before you commit

From the edge, with a flashlight held low so the beads glint, decide whether this is a small spill: one device's worth from the table above, on a hard floor or short-pile surface, nothing in a floor register or duct, not on a hot surface, and nobody pregnant and no young child living in that room. The reason: the method below works on hard surfaces and small quantities and nothing else. If any condition fails, stop collecting, keep the room closed and ventilating, and call the local health department or your state environmental agency for direction. Beads in carpet pile, a register or a crack you would have to dig into are past this method, and digging turns one bead into many.

Step 4: Dress for contact, and leave the respirator decision where it belongs

Take off rings and watches (gold and silver amalgamate with mercury, and a ring that touches it is ruined), put on nitrile gloves, and bag your boots. The inhalation route is managed by steps 2 and 3, short work and outdoor air; a respirator for mercury vapor is a 29 CFR 1910.134 program question with cartridges rated for it, not something to improvise from a dust mask, which does nothing for a vapor. See related: How to Decide Whether a Task Needs a Respirator.

Step 5: Collect without splitting

Glass first, lifted by hand onto a damp paper towel. Then beads, pushed slowly together with two stiff cards so small ones merge into larger ones, rolled onto a card and tipped into a wide-mouth jar with a screw lid; an eyedropper takes the ones too small to push. Then wide tape pressed over the area to lift what you cannot see. Check from three low flashlight angles until nothing glints. The reason: each move gathers rather than divides. Skip the tape and the droplets too fine to see stay on the floor, still evaporating. The full sequence with acceptance and stop rules for every step is in the shop procedure; see related: The Small Mercury Spill SOP.

Step 6: Separate the debris from the device

Two containers, not one. Everything that touched loose mercury (beads, glass, cards, tape, gloves, boot bags, towels) goes in the sealed debris jar. The rest of the device, and any switch that did not break, goes into the shop's closed container for mercury-containing equipment. The reason: they leave the shop by different routes, explained below. Skip it and a box of intact thermostats headed for a recycler carries loose spill debris it was never accepted for.

Step 7: Close the room out and tell the customer

Ask the customer to keep the room's windows open, the door closed and the HVAC off for at least 24 hours, and tell them plainly what broke, roughly how much, what was collected, whether anything was left in place, and that the local health department can check the air. Wipe your soles with a damp towel, bag it, and only then get back in the van.

Step 8: Send each container down its own waste route

This is where the job is usually lost, weeks later, in the back of the shop.

The intact device is universal waste. Under the federal universal waste rule at 40 CFR Part 273, thermostats and other mercury-containing equipment can be managed under lighter rules than full hazardous waste. A shop that accumulates less than 5,000 kilograms of universal waste at any time is a small quantity handler: it keeps the devices in a closed, structurally sound container, labels it with the words the rule specifies (for example "Universal Waste - Mercury Thermostats"), can show how long each item has been held, and sends it to a recycler or destination facility within one year. A device that is leaking must be put in a closed container that holds the leak. Several states layer more on top, including thermostat collection laws that require contractors removing mercury thermostats to send them to a recycling program rather than the trash, so check your own state's rule. See related: Universal Waste Explained for a Service Shop.

The spill debris is not, by default. The universal waste rule requires a handler to contain a release and to determine whether the cleanup material is hazardous waste, which mercury debris usually is. Whether debris from a customer's home falls under the household exemption or counts as the shop's own waste is a determination states answer differently. Before the jar goes anywhere, call your state environmental agency's hazardous waste assistance line or the local household hazardous waste program and ask which route applies to you, and record the answer. Never into the dumpster, never down a drain.

Worked example: a thermostat dropped in the garage

A tech removes an old two-switch heat pump thermostat from a hallway wall, sets it on the box lid and carries it out through the attached garage. It slips and lands on the concrete floor; one switch capsule breaks, the second stays whole inside the body. The garage is about 40 F, the overhead door is closed, and the customer's teenage son is standing by the workbench.

• Steps 1 and 2: the son goes inside and the house door is closed behind him. There is no forced air in the garage, so the tech opens the overhead door and the side door and waits 15 minutes outside. The cold helps; it does not shorten the wait, because the 15 minutes is the method's interval, not a temperature calculation.
• Step 3: one switch, on bare concrete, no register, no young child or pregnant occupant in the garage. Small. One bead has rolled into a control joint in the slab.
• Step 4: wedding ring off into a pocket, nitrile on, boot bags on.
• Step 5: glass onto a damp towel and into a jar, then the cards gather the droplets into four beads, all tipped in. The bead in the control joint sits below the surface of the cut. Prying it out with a screwdriver would split it, so the tech presses tape over the joint instead; it lifts the bead on the second try. Two further tape lifts come up clean, and three flashlight sweeps show nothing.
• Step 6: the debris jar is lidded, taped and labeled as spill debris with the date and address. The thermostat body, with its intact switch, goes into the shop's closed thermostat container, whose label already carries the accumulation start date from the first unit it received.
• Step 7: the customer is told one of two switches broke, a few grams at most, all collected including one bead from a slab joint, garage doors to stay open for the afternoon and the house door closed, and the health department's number for an air check if they want one.
• Step 8: back at the shop the office calls the state hazardous waste assistance line about the jar and logs the answer and the call date on the job. The thermostat container has been accumulating for five months, inside the one-year limit, and is scheduled for the recycler with the next pickup.

What would have changed it. Had the tech grabbed the customer's shop vacuum from the bench, which is what the son offered, the answer would have flipped at step 3: a vacuum run over mercury is itself contaminated, goes unplugged and untouched into the closed garage, and the call to the health department happens before anything else. The same is true if the dropped unit had been one of the old U-tube manometers some boiler rooms still have mounted on the wall: that is tens of grams or more, outside the small-spill method from the start.

References

• US EPA, guidance on cleaning up a broken mercury thermometer and on mercury spills in the home
• 40 CFR Part 273, Standards for Universal Waste Management (mercury-containing equipment, small quantity handlers)
• 40 CFR 302.4, CERCLA reportable quantity for mercury; 29 CFR 1910.1000 Table Z-2
• See related: The Small Mercury Spill SOP; Mercury Thermostats, Switches and Gauges
• See related: Universal Waste Explained for a Service Shop