Paint thinner is super useful for getting the most out of paint, particularly when it’s been laying around for a while or when you want to thin out the paint to use in a sprayer. It is also commonly used for cleaning up spilled paint or to clean paintbrushes. But is it also a major fire hazard for your home or office? If so, what can you do to make sure that when you use paint thinner, you do so safely?
Paint thinner (mineral spirits) is a flammable liquid, as classified by OSHA. Since it can catch fire and has a flashpoint below 199.4 degrees Fahrenheit (93 Celsius) it is considered a flammable liquid. The flashpoint of paint thinner is around 104 degrees Fahrenheit.
Care should be exercised with flammable liquids. Let’s take a look at paint thinner and fire safety.
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Also read: What Makes Something Flammable?
Are Mineral Spirits Flammable?
When most people ask if something is flammable, they just want to know if it will catch fire.
However, there is a technical distinction regarding flammable liquids that classify how easily something will burn.
Paint thinner (mineral spirits) will catch on fire somewhat easily.
OSHA (Occupational Safety and Health Association) outlines this criteria in Standard 29 CFR 1910.106.
It states that a liquid is classified as a flammable liquid if it has a flashpoint at or below 199.4 degrees Fahrenheit (93 degrees Celsius) and as a non-flammable liquid when the flashpoint is above 199.4 degrees Fahrenheit.
This table may make it more clear:
| Flammability Classification | Flashpoint |
|---|---|
| Flammable Liquid | Flashpoint < 199.4 degrees F (93 C) |
| Non-Flammable Liquid | Flashpoint > 199.4 degrees F (93 C) |
Non-Flammable liquids still may catch fire, they just need higher temperatures to do so.
The flashpoint is the temperature at which a liquid gives off enough vapors to ignite when exposed to an ignition source.
Also read: Is PVC Pipe Flammable? Is it Fire Resistant?
What Is The Flashpoint?
The flashpoint of paint thinner is typically given as 40 degrees Celsius or 104 degrees Fahrenheit, which is a bit warmer than the average healthy human being (98.6 degrees F).
However, this is not the whole story and depending on the brand and the exact circumstances, there is a range of flashpoints that runs from 73.4 to 140 degrees Fahrenheit (23 to 60 degrees Celsius).
As you can see this makes working with paint thinner can be hazardous as it doesn’t have to be that hot for it to be susceptible to fire, if there is an ignition source, such as a spark or flame.
Also read: Is Paint Flammable/Combustible?
Can It Spontaneously Combust?
Yes, paint thinner (mineral spirits) can spontaneously combust or catch fire when it reaches the auto-ignition temperature of 245 degrees Celsius or 743 degrees Fahrenheit.
That is, it can catch fire even with no discernible spark or ignition source. This makes how you handle and then store and dispose of paint thinner an important issue.
Also read: Is Turpentine Flammable? Flashpoint
Can It Catch On Fire Easily?
Yes, in fact, paint thinner can very easily catch on fire – even though it is not a flammable liquid, by OSHA standards. Under no circumstances should you work with paint thinner near sources of ignition or smoke near it.
Take a look and see what happens when paint thinner meets fire…
Are The Fumes Flammable?
Yes, paint thinner fumes are flammable (actually combustible, but yes, they will catch fire). Actually, that’s the only part that is flammable.
When a liquid burns, it is not the actual liquid that is burning. Liquids give off fumes (turn into a gas) at different temperatures depending on the type of liquid. These fumes are what burn.
This means that you need to pay attention to the fumes as a hazard when working with paint thinner. That means, ideally, working outdoors or in a place that is extremely well-ventilated.
However, if working outside – you need to take precautions to ensure that the paint thinner is never in direct sunlight, as the flashpoint of paint thinner is low enough that this could cause fire if there is an ignition source.
Also read: Is Pepper Spray Flammable?
Is It Flammable When Dry?
In general terms, once paint thinner has “dried” it has evaporated and that means there is no more paint thinner, and so, “dry” paint thinner is not in any way flammable because you can’t burn what isn’t there.
However, it is important to realize that in rooms with poor ventilation – the fumes are likely to still be present in the air rather than being spread out and diluted. These fumes are absolutely still flammable and it’s why you should always work with paint thinners in well ventilated areas.
Also read: Is Acetylene Flammable?
How To Store Paint Thinner Safely
The container in which the paint thinner is to be stored should be tightly sealed because paint thinner fumes are as flammable as paint thinner itself. Leakage over time could cause the storage area to become highly flammable.
It would also make it a dangerous place to work as breathing paint thinner fumes for any lengthy period of time is definitely not advisable.
If you have more than a small container of paint thinner, then you should be aware that as a Category 3 flammable material – it ought to be held in a safety cabinet.
You may keep up to three such safety cabinets in any given area and each safety cabinet may hold no more than 60 gallons of paint thinner. Source.
Safe Disposal
Paint thinner must not be poured down the drain or dumped in a dustbin because it can contaminate water.
If you are working on a commercial site, the paint thinner should be disposed of in an Oily Waste Can which is designed, specifically, for flammable waste.
These waste cans can then be disposed of by a professional waste management company and in the interim they provide an airtight seal which ensures that no fumes can escape the can and no sources of ignition may enter it.
At home, the best thing to do is exhaust the paint thinner completely, then after an hour or so with the lid off in a shaded and cool outdoor location, you can be sure that it has all gone and the empty bottle can then be discarded as household waste.
Also read: Is Fiberglass Flammable or Fire Resistant?
Conclusion
As you can see, paint thinner can ignite at just 40 degrees Celsius or 104 degrees Fahrenheit. Because it is flammable, caution should be exercised when using this liquid.
You should always use paint thinner outdoors or in a very well-ventilated space, if you are working with it for a long period of time – you might want to consider using a respirator too as it gives off fumes. When it’s not in use, you need to store paint thinner in a way to minimize the chances of a spark or a flame coming into contact with it and containers must be kept firmly closed.
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