Considerations for Galvanization

Galvanization

Galvanization is the process of applying a protective coating of zinc to steel or iron to prevent rusting.

The most prevalent process for galvanization is called hot-dip galvanization where the steel is dipped into a vat of molten zinc to apply the coating.

During the process the zinc bonds to the iron in the steel (steel being an alloy of iron and carbon). The bond occurs in layers.

With each subsequent layer, the composition of that layer changes. As you get closer to the steel, the amount of iron in the layer increases and the amount of zinc decreases.

The outermost layer of the galvanization is 100% zinc.

Risk Analysis

If we are going to play with barbed wire with galvanized coating, does the galvanized coating increase our risk?

If so, what is the risk?

How could that risk be mitigated or eliminated?

Possible Scenarios:

  1. Galvanized coating (zinc or zinc-alloy) is compromised somehow, becomes detached from the barbed wire, and is introduced into the body.

    a. Introduction of zinc particles subcutaneously via barb stick.

    b. Incidental oral ingestion of zinc particles.

    c. Incidental inhalation of zinc particles.

  2. Allergic reaction to the coating due to contact with the galvanized coating.

How likely is the galvanized coating on the barbed wire to be compromised during prep? During play?

Galvanization and Heat

“Constant exposure to temperatures below 390°F (200°C) is a perfectly acceptable environment for hot-dip galvanized steel.”ˢᵒᵘʳᶜᵉ

Steam autoclave sterilization usually reaches temperatures between: 248 - 275°F (120 - 135°C)

Dry heat sterilization techniques usually utilize temperatures around: 340°F (170°C)

In my estimation there is no reason to believe dry heat or steam sterilization poses any risk to the structural integrity of galvanized coating on barbed wire.

Galvanization and Chemicals

“Zinc is most useful in solutions with pH 5.5 - 12 and less useful in acidic or strongly alkaline chemical environments encountered, for example, in the chemical process industries. Corrosion of zinc increases rapidly in aqueous chemical solutions on either side of the pH 5.5 - 12 range.”ˢᵒᵘʳᶜᵉ

Here is a list of common chemicals you might decide to use on your barbed wire and their pH values:

pH Chemical
1 - 2 Muriatic Acid
2 Vinegar
3 - 6 Hydrogen Peroxide
5.5 - 7 Chlorhexidine Gluconate
6 - 8 Isopropyl Alcohol
12 Soapy Water
13 Bleach

The takeaway is that chemicals within a certain pH range can compromise the integrity of the galvanized coating.

In fact, one of the most common ways to remove galvanized coating from galvanized steel is via chemical stripping using lower pH acids. For non-industrial uses vinegar is effective, but is known to take a while.
More effective is Muriatic Acid.
Muriatic acid is a diluted form of hydrochloric acid that is available for purchase at your local big box hardware store. Muriatic acid is used for cleaning masonry, removing mold, and is often used to correct the pH balance in swimming pools.
Care should be taken when using muriatic acid to remove coating from galvanized steel, as muriatic acid is a strong acid that itself can harm the user but also the resulting chemical reaction produces a significant amount of heat and toxic fumes (zinc oxide).

Using vinegar to strip the coating is considered much safer, but is also much less efficient, as such it takes significantly longer.

Zinc Patina, Zinc Oxide & Zinc Carbonate

Zinc Patina

Freshly galvanized steel, when exposed to wet and dry cycles, will develop a natural coating known as zinc patina.

This patina goes through stages, it starts as a thin layer of zinc oxides, then exposure to moisture turn the zinc oxides into zinc hydroxide [Zn(OH)2], then when the zinc hydroxide is dried it is converted to zinc carbonate.

In typical, outdoor environmental conditions, this process takes 6-12 months to develop.

It is best practice that when playing with barbed wire, you play with new, unused barbed wire that has not been previously exposed to outdoor environmental conditions such that the patina process would be a risk. It has been posited that if barbed wire were to be autoclave sterilized or a specific regiment of cleaning and drying were used in the sanitation process it may be possible to recreate the conditions required for patina development.

In my estimation, this is extremely unlikely, but it is also impossible to rule this out as a risk.

Zinc Oxide Inhalation

When galvanized steel is heated to extremely high temperatures, the coating breaks down and the zinc is converted into zinc oxide vapor.

Inhalation of sufficient quantities of zinc oxide vapors will cause a severe flu-like illness commonly known as Metal Fume Fever (MFF).

These concerns are common among metalworkers, specifically welders who work with galvanized steel.

Welding of steel occurs at temperatures that far exceed the temperatures discussed in the above Galvanization and Heat section by orders of magnitude.

In my estimation, again this seems like a very minute risk but one that can’t be completely discounted definitively.

Toxicity Risk

“Zinc is an essential trace metal with very low toxicity in humans”ˢᵒᵘʳᶜᵉ
For zinc ingestion to be toxic, high amounts must be ingested, in excess of 50 mg. 

In my estimation, the likelihood that incidental ingestion of a minute quantity of elemental zinc particles by itself would cause illness without the presence of other exacerbating medical or environmental conditions is low.

Summary

  • Galvanization adds a coating of zinc to barbed wire.

  • It is possible to compromise the coating via chemicals (of a certain pH value) or mechanical means.

  • Zinc is a trace metal with very low toxicity in humans in elemental form.

  • Zinc only becomes considerably toxic when subjected to extremely temperatures and the resulting fumes of zinc oxide are inhaled.

  • Heat sterilization methods do not utilize temperatures hot enough to create zinc oxide.

  • Several of the chemicals we might use to sterilize or disinfect barbed wire can compromise the coating, however none of the chemicals are known to chemically react with zinc to create zinc oxide.

References