Are Mothballs Flammable or Combustible?

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Mothballs were once ubiquitous, nearly every household had mothballs in every closet to try and keep the insects away from their clothes. We see them much less often today, because we tend to replace our clothes more regularly, our houses are often air-conditioned (and thus, hostile to insect life), and because of other changes in modern life. But are mothballs a fire hazard and if so, should we have them under any circumstances?

Mothballs are flammable. The modern mothball is made from 1,4-dichlorobenzene, rather than the traditional naphthalene. Some say this is because naphthalene is highly flammable, all we can say is that 1,4-dichlorobenzene has exactly the same NFPA 704 code for flammability. Both types are flammable.

Lets take a look at what mothballs really are and their fire safety concerns. Check it out.

Also read: What Makes Something Flammable?

What Are Mothballs? 

are mothballs flammable?

A mothball is a small brick or ball of pesticide. They were designed to help with the storage of clothing to prevent mold from forming on the clothes and to ensure that clothes moths and other insects wouldn’t breed in the clothing and consume it. 

The mothball was originally made from a chemical known as naphthalene, but in recent times this has been replaced by 1,4-dichlorobenzene. Oddly, though these chemicals are quite different, they both have the same strong, sweet, and slightly sickly smell that most of us associated with mothball usage. 

And both of these chemicals undergo a unique chemical process known as “sublimation”. That means that when they get hot, they don’t melt, but go straight from a solid into a gas – it is this gas that makes them deadly to insects (and moth larvae, in particular). 

There are some concerns that this reaction isn’t very good for human beings though and you may occasionally find mothballs that are made from camphor too.

For the purposes of this article, we’re not considering camphor mothballs as you’re unlikely to have these in use in your home. 

Mothballs must also be stored in a plastic bag, which won’t react with the mothball (this means polyethylene or polypropylene) and in a dark, cool place when not in use. If you don’t follow this protocol, it’s entirely possible the mothballs will sublimate completely before you can use them. 

You may only use a mothball in the manner detailed on the package, as other uses are often completely illegal in North America.

It’s also worth noting that the US Department of Health and Human Services considers 1,4-dichlorobenzene to be a potential carcinogen and long-term exposure to naphthalene is no good for your health, either. 

Can They Catch Fire?

Yes, mothballs are combustible and can catch fire. When the vapor is given off from a mothball, that vapor is flammable. This happens at 174 degrees Fahrenheit (79 Celsius).

This is because the ratio of mothball chemical to oxygen is dramatically different when a mothball is in vapor form compared to solid form. 

This means that mothballs can be a serious fire hazard in the home.

This is particularly true if you are storing large amounts of mothballs together – a leak in the packaging could allow vapor to escape and build up in one place. 

Because of this, you should try to ensure you don’t store very many mothballs and that those you do store are in a cool, dark, and well-ventilated space. 

You can see what happens when both naphthalene and camphor mothballs are lit on fire here:

EXPERIMENT Fire Vs Mothball Vs Camphor

What Happens If They Are Left In Direct Sunlight?

In most cases, if you leave mothballs in direct sunlight, the energy from the sunlight is enough to trigger this process of sublimation. Over a period of about 30 minutes, you are likely to see all of the mothballs effectively evaporate in direct sunlight and there would be nothing left. 

As we’ve already seen, mothballs are capable of sublimation – that is they change from a solid into a gas with no intermediary liquid stage.

Are They Ever Explosive? 

Mothballs in their solid-state are not explosive – they are combustible (which means you can light them on fire,) but they usually won’t cause explosions. 

In their vapor state, however, the vapor can be explosive.

If you were to trap enough vapor from mothballs in a confined space and then introduced a flame, you would find that you risked an explosion and the heat from that explosion could set fire to any remaining solid mothballs too. 

What About Naphthalene Balls?

No, naphthalene mothballs are not flammable, but they are combustible, just like 1,4-dichlorobenzene mothballs are. They can catch fire but the flashpoint is above 100 degrees Fahrenheit.

They are considered an explosive hazard when in vapor form.

If naphthalene mothballs do catch fire, you can tackle the resulting blaze with dry chemicals, CO2 extinguisher or a water spray. 

Is It Safe To Keep Them In The House?

There are two things to consider when it comes to wondering whether it’s safe to keep mothballs in the house.

Firstly, there’s the fire risk.

While not “flammable” in the strictest sense, mothballs are a genuine fire risk and we wouldn’t recommend, on this basis, keeping any more mothballs on hand than you absolutely need for pest control.

Secondly, there are appreciable health risks associated with the use of mothballs.

While we’re not qualified to determine how serious those risks are, there are many articles on the internet such as this one by Gwen Spicer, that assert that the risks are serious enough that nobody should use mothballs at all.

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