How Do You Measure the Fire Resistance of Galvanized Steel?
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In our blogs, we have consistently repeated the praises of galvanized steel. Its corrosion-resistance means it can survive even the most challenging environments, enabling some structures to last 70 years or more.
But what about the fire resistance of galvanized steel?
You may not be aware that the protective zinc coating plays a large role in establishing the level of fire resistance of galvanized steel. In this article, we’ll review some common questions about zinc’s role and how you can measure the fire resistance of galvanized steel.
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How Do You Measure the Fire Resistance of Galvanized Steel?
One of the measurements of the fire resistance of galvanized steel is based not only on how well the surface absorbs heat, but also how long the steel can withstand fire.
It’s measured in minutes, so for example, a rating of R15 means that the steel can withstand fire for 15 minutes before it becomes in danger of structural failure.
Typically most regular buildings (like warehouses) need an R30 rating, which translates to 30 minutes.
Is Galvanized Steel Fire-Resistant?
Galvanized steel is well-known for its ability to resist corrosion thanks to its zinc coating. But researchers have discovered other benefits as well.
While technically it’s not classified as fire-resistant per se, galvanized steel protects the structural properties of steel. However, zinc protection only lasts up to certain temperatures.
The zinc helps the steel heat up more slowly in the event of a fire. The zinc “bounces” the heat away from the bare steel.
When steel gets hot, it can lose a lot of its strength. Therefore, the slower heating thanks to galvanization helps the steel stay stronger in the event of a fire—at least up to around 932 degrees Fahrenheit.
While this may not be useful for all environments – such as large apartment buildings—it’s ideal for structures that only need to survive a fire for 15 to 30 minutes, like a parking garage or warehouse.
What Does Fire Resistance Mean for Building Standards?
ASTM E119, is used as the industry standard for measuring how long items such as walls, floors and beams can withstand a fire.
It then assigns it a fire-resistance rating.
Remember: galvanized steel means that the steel has a zinc coating. Zinc and steel behave differently under intense heat.
Can Fire Impact the Zinc Coating on Galvanized Steel?
Yes, fire can affect the coating.
Zinc melts at around 787 degrees Fahrenheit. Once it begins to melt, it can no longer effectively reflect the heat. This also means that around 932 degrees Fahrenheit, the zinc behaves in the same way as the steel beneath it.
In addition, evaluating the impact on the zinc coating can present some inspection challenges because fire-damaged galvanized steel may look intact but have a compromised coating.
Are There Any Advantages of Using Galvanized Steel for Fire-Resistance?
Yes, although these advantages do not mean it can be a substitute for materials that are specifically built for fire resistance.
However, some of the benefits include:
- Galvanized steel is non-combustible: It doesn’t “feed” the fire like wood does.
- Short-duration integrity: If the fire is brief or lower in intensity, steel may be able to retain some of its load-bearing characteristics.
- Post-fire corrosion resistance: If the zinc coating survives, it can still help prevent rust effectively after a fire.
Can You Use Fireproofing Techniques on Galvanized Steel?
Yes, there are several techniques you can use. These include:
- Coatings: Intumescent coatings can expand when they are exposed to heat. The result is an insulting layer.
- Cementitious sprays: These work by delaying the heat transfer to the steel.
- Board systems: These are implemented by using fire-resistant boards to encase steel sections.
It’s important to note that adding these additional protective measures does not interfere with the zinc coating’s corrosion resistance.
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Key Takeaways:
- Galvanized steel has roughly half the heat absorption rate of bare steel, meaning it stays cooler longer in a fire.
- Fire resistance is measured in minutes, with most common buildings like warehouses requiring a 30-minute (R30) rating.
- The zinc coating helps steel heat up more slowly, keeping it stronger during a fire — but only up to around 932°F.
- Zinc melts at around 787°F, after which it can no longer reflect heat effectively.
- Above 932°F, the zinc behaves the same as the bare steel beneath it, losing its protective advantage.
- Fire-damaged galvanized steel can look fine on the outside but have a compromised zinc coating underneath.
- Galvanized steel is non-combustible, meaning it won’t fuel a fire the way wood does.
- Additional fireproofing methods like intumescent coatings, cementitious sprays, and board systems can be added without harming the zinc coating’s corrosion resistance.
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Sources:
Galvanizers Association (UK), “Fire Resistance of Galvanized Steel,” https://galvanizing.org.uk/galvanized-steel-fire-resistance/
American Galvanizers Association, “Fireproofing HDG Steel,” https://galvanizeit.org/knowledgebase/article/fireproofing-hdg-steel
