Flash Point
The lowest temperature at which a liquid gives off enough vapor to ignite in air, if something is there to ignite it. It is a property of what is evaporating rather than of the liquid itself, which is why it matters far more for some coating products than others.
What flash point measures
Flash point is the lowest temperature at which a liquid gives off enough vapor for that vapor to ignite in air, if there is something present to ignite it. The important word is vapor: the figure describes what is coming off the surface of the liquid, not the liquid burning.
That distinction has a practical consequence. A product sitting at or above its flash point is not on fire and will not start on its own. It is in a condition where an ignition source would find something to catch. So there are two levers, not one, and removing sources of ignition is as much of the answer as controlling temperature.
It is a property of the solvent, not of the coating
This is the part that decides whether the number matters on a given day. Vapor has to come from somewhere, and in a coating it comes overwhelmingly from the solvent.
A hundred percent solids epoxy has very little to give off, so it produces little vapor and its flash point sits well above anything a jobsite reaches. The products on the same van that behave differently are the solvent borne ones: a solvent based primer or sealer, a thinner, and whatever is being used to clean tools and wipe up. Those are the tins to check, and checking them is a different habit from checking the coating.
The situation worth thinking about in advance
The combination that deserves attention is solvent vapor and an open flame in the same enclosed space, and the ordinary route to having both at once is cold weather.
A slab too cold to coat has to be warmed, and the dew point rule is usually what tells you so. The fastest tool for the job is often a direct fired propane or kerosene heater, which is an open flame sitting at floor level. Most solvents used in coating work give off vapor that is heavier than air, so it does not rise away and thin out; it travels across the floor. The heater is taking its air from precisely where the vapor has gone.
None of that is an argument against warming a slab, which is often the right call and sometimes the only one. It is an argument for knowing which products in the van are solvent borne before deciding how to heat the room, because that is a choice made early and hard to revisit once the equipment is running. It is worth noting that our own dew point guide already warns about unvented heaters for a completely different reason, which is the water they add to the air. Both cautions are about the same piece of equipment and neither replaces the other.
Where the number lives
On the safety data sheet, which is not the technical data sheet. The two documents have different jobs: as our data sheet guide puts it, the technical sheet tells you how to use a product and the safety sheet tells you how it can hurt you and what to do about it. Flash point, storage and disposal all sit on the second one.
It is a common gap to have studied one of those documents closely and never opened the other. If a product is solvent borne, the safety sheet is the one holding the numbers this page is about, along with the instruction for how its soaked rags and leftovers should be stored and got rid of. A heap of solvent rags left in a warm corner at the end of a day is the situation those instructions exist for.
This page deliberately prints no temperatures. Flash points differ by product and by formulation, a figure given here would be read as covering a whole class of products, and it is the kind of number somebody might act on. The sheet for the tin in front of you is the only authority worth using.
Frequently Asked Questions
Does epoxy have a flash point I need to worry about?
Usually the resin itself is not the concern. A hundred percent solids epoxy has nothing much to evaporate, so it gives off little vapor and its flash point is high enough that ordinary jobsite conditions will not reach it.
The things on the same job that do have low flash points are the solvents: a solvent borne primer or sealer, a thinner, and whatever is being used for cleanup or for wiping tools. Those are the products to check, and the number is on the safety data sheet rather than the technical one.
What is actually the risk on a floor job?
The combination that deserves attention is solvent vapor and an open flame in the same enclosed space, and the usual way both end up there at once is cold weather.
A slab too cold to coat gets warmed, and the quickest tool is often a direct fired propane or kerosene heater, which is an open flame at floor level. Most common coating solvents give off vapor heavier than air, so it does not rise and disperse, it spreads across the floor. The heater is drawing air from exactly where the vapor is.
That is not a reason never to heat a slab. It is a reason to know which of the products in the van are solvent borne before deciding how to warm the room.
Is flash point the temperature the liquid catches fire at?
Not quite, and the distinction is worth having. Flash point is where the liquid produces enough vapor for that vapor to ignite from a source such as a flame or a spark. It is a statement about the vapor above the liquid.
So a product at or above its flash point is not burning and will not spontaneously start. It is in a state where an ignition source would find something to catch. Removing the ignition source is therefore as much of the answer as controlling the temperature.
Where do I find the flash point for a product?
On the safety data sheet, not the technical data sheet. Those are two different documents with two different jobs: the technical sheet tells you how to use the product, and the safety sheet tells you how it can hurt you and what to do about it.
It is a common gap on site to have read one carefully and never opened the other. If a product is solvent borne, the safety sheet is the one carrying the number you need.
What about the rags and the waste?
Solvent soaked rags are worth handling deliberately rather than dropping in a pile or a bin liner at the end of the day. They hold solvent, they keep giving off vapor, and a heap of them in a warm corner is the wrong place for that to happen.
The safety data sheet for whatever you were using will state how it should be stored and disposed of, and that instruction is written for exactly this situation.