Jump to content
Sign in to follow this  
bilgerat

Boiling Galvanized tubs

Recommended Posts

Question:

 

It was recently suggested that we boil our cleaning water directly in the galvanized tubs we use at our cleaning station.

 

We tried it and it worked great.

 

However, a concern has been raised about possible health issues resulting from heating galvanized materials (zinc issue).

 

Does anyone have any solid info on this?

 

Can you point me to a reliable source on the subject?

 

Thanks!

Share this post


Link to post
Share on other sites

You can find lots of medical info on line (thank you Google and Yahoo) frinstance http://www.finishing.com/71/64.shtml and

http://www.finishing.com/217/03.shtml and http://answers.yahoo.com/question/index?qid=20080226173711AANCXL0

 

Hot soapy water in an old galvanized tub? No danger there. Once the soap has washed off the "finishing oil", and the dishes are rinsed off, there should be no toxic residue.

However, in woodfire heating the tub, you risk producing zinc and/or lead and/or other metalic fumes that could be irritating and toxic. See "foundry flu" or "fume flu".

Old wash board and wash tub images...

 

 

Share this post


Link to post
Share on other sites

Heating water in a galvanized tub is no problem. You only get the fumes when you go to a molting stage of the metal. Which is something you won't get from heating a tub of water no mater your heat source.

 

If you can get enough heat from a wood fire to melt the tub you have a really hot fire and with water in the tub you will never get it that hot no matter how hard you try

Share this post


Link to post
Share on other sites

scr - well it's possible to generate zinc fumes over a campfire. But the big question is, will you generate zinc fumes over a campfire.

 

First, we need to understand what galvanized steel is. It's essentially steel or iron bathed in melted zinc which chemically bonds to the steel or iron to help prevent rust.

 

Second, we need to understand gasification. In order to put out any fumes (which is the gas state of matter), a solid like zinc has to first be turned to a liquid state, then has to be heated up enough to start the gasification process. Think ice to water to steam. Ice (solid) puts out no fumes. Left to melt to water (liquid), water, without being heated, puts out no fumes (steam - the gas state of water). Bring a pot to boiling and at some point, the water will start to put out fumes (steam), and usually before it reaches the boiling point.

 

The melting point of zinc is 787.24396 degrees Fahrenheit.

 

The boiling point of zinc is 1,664.6 degrees Fahrenheit.

 

At some point between those two temperatures, zinc will start to put out fumes (the gas form of zinc). We know that campfires can get to at least 800 degrees Fahrenheit - the melting point of lead - in the revolutionary war, people melted lead over campfires to make bullets. Depending on the wood used, campfires can reach about 1,800 degrees Fahrenheit. Zinc falls well within that range. So, according to the science, yes, you could conceivably create zinc gas over an open campfire.

 

However, the zinc is chemically bonded to another metal - usually iron, and the melting point of iron is 2,750 degrees Fahrenheit. The question becomes, will you be able to heat the zinc enough to force it to lose it's chemical bonds with the iron? Probably not at the lower range of the temperatures needed to turn and keep zinc liquid, but potentially at the upper range of those temperatures, and even then, it's just as unlikely to melt as it is likely to melt. Aluminum melts at about 1,220 degrees Fahrenheit - if your fire won't melt aluminum, you're probably safe. If you're building fires that reach 1,800 degrees Fahrenheit, then you might want to take a look at your fire building practices.

 

Of course this all assumes that you're putting the tub on the fire empty. As Gary mentions, there is an added element here - water in the tub. And water heats to boiling in the tub by absorbing the heat of the vessel its in, until it reaches its boiling point. Even after the water reaches its booiling point, the metal still isn't going to start increasing in temperature until all the water has turned to steam. So even if your fire is hot enough to cause zinc to melt, until the vessel no longer has water to push as much heat as possible in to, the zinc won't reach its melting point.

 

I'd say you're probably safe to boil your water in your galvanized tubs over an open flame but if it truly becomes an issue, then use your camp stoves. You can probably try to explain the science to those who are worried, but they won't listen because they've already been told that zinc fumes can be created and are dangerous. Of course, dollars to donuts they also take zinc tablets when trying to fight off a cold, but hey, why go there.

Share this post


Link to post
Share on other sites

Technical detail..."Fume" is actually a fine particle resulting from the condensation of a metal vapor. A metal is heated, melts to a liquid, vaporizes to a gas, and almost immediately condenses in the cold air to a particle. Welding on galvanized commonly can cause "metal fume fever" resulting from inhaling the zinc. I agree, typical camp stoves and camp fires will not achieve these temperatures.

Share this post


Link to post
Share on other sites

I agree that the dangers of zinc poisoning are slim.

 

On a side note.....how big are these tubs?

 

I'm picturing a #2 washtub and thinking it's gonna take an hour or two to get this water to even boil.

Share this post


Link to post
Share on other sites

Well done CalicoPenn!

Even I who when it comes too chemistry am a real duffer, managed to understand what you explained.

That was great!

Eamonn

 

Share this post


Link to post
Share on other sites

Thanks for the great detail in the replies.

 

We boil our water over a Turkey Fry burner and usually have used the Frying pot; however, this method of heating the water directly in the washtubs (I don't know the official #, but they are about 18 inches across - three in our wash station (one for soapy water, one for bleach, and a cold water rinse tub).

 

 

Share this post


Link to post
Share on other sites

Additional Question.

 

I have seen Troops make "trash-can" Turkey where they take coals, a turkey on a spit, and place a trash-can (which I presume is galvanized steel straight from China) over it. Cooks for hours. I know the trashcan gets too hot to touch.

 

Is there a zinc hazard there?

Share this post


Link to post
Share on other sites

>>I have seen Troops make "trash-can" Turkey where they take coals, a turkey on a spit, and place a trash-can (which I presume is galvanized steel straight from China) over it. Cooks for hours. I know the trashcan gets too hot to touch.

 

Is there a zinc hazard there?

Share this post


Link to post
Share on other sites

While I agree with Calico's description, I also note that all water is not the same. If you check the web for the technical aspects of municipal water treatment you will see that in some areas of the country, water tends to 'corrode' or 'erode' pipes differently from other areas. This is because of the dissolved materials in the water, or lack thereof.

In my area water actually tends to slowly dissolve copper or brass pipes whereas in nearby areas with greater concentrations of dissolved materials, those same pipes may experience the buildup of precipitates.

A galvanized container may release zinc into hot water in a manner that is dependent on the characteristics of the water.

However, while I would not use one of these for cooking soups or stews, I would not worry too much about cleaning water. I merely wonder why bother with a galvanized container in the first place? Why not aluminum or stainless steel for cleaning. You'll never have to worry about rust for either of those and you can use the stainless for cooking to boot!

Share this post


Link to post
Share on other sites

>>I merely wonder why bother with a galvanized container in the first place? Why not aluminum or stainless steel for cleaning. You'll never have to worry about rust for either of those and you can use the stainless for cooking to boot!

Share this post


Link to post
Share on other sites

The zinc on the surface of the pan oxidizes quickly. This ZnO has a decomposition point of 1975C which you are very unlikely to get to with a campfire. Carbon does reduce this so it might be possible to melt it using it as a fire pan.

 

ZnO is relatively insoluble in water and has a low toxicity when consumed, you would need to eat large quantities to have any risk. You expose yourself much more with ZnO based sunblocks. Breathing it could be an issue, which is why your should wear a respirator when working where dust is potential. Getting zinc poisoning from cooking a turkey in a garbage can or boiling water in a tub is very unlikely.

Share this post


Link to post
Share on other sites

I would only question the washtub based on the source of the washtub (country of origin).

 

A galvanized tub from China could (and probably does) have all kinds of non-zinc components in the coating...and the tub for that matter.

 

They don't exactly know about quality control, or safety.

 

For example, if the galvanization is contaminated with Zinc Chloride, the melting point drops significantly to 565 F.

 

Zinc Hydroxide melts at a lower temp of 257 F.(This message has been edited by Engineer61)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×