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The mechanics of Passive Fire Protection

Apr 01, 2020

Through our recent blogs we have looked at hydrocarbon and cellulosic fires, discussed the future of fire rating, and how building materials are changing the face of construction. Yet, it has been a while since we discussed the technical background for one product, we believe is a leader in the field of thin-film intumescents — SC902.
So today, we thought we would take a look into:

  • The background of thin-film intumescents;

  • How they work;

  • Give you some top level insight into chemical reactions and how they work; and

  • Why they have advantages over other alternatives.

What are intumescents?

Let’s start at the top and answer the timeless question – what are intumescents? Simply put, intumescents are a form of thermal protection material first introduced to market in the 1980s. They are applied as a coating to structural steel to delay the transfer of heat into the steel due to an increase in temperature due to flame.  
They are known by a number of names, including but not limited to fire-proof paint, intumescent paints or coatings, fire rating coating, and the many others. Furthermore, they can be water-based, solvent-based, epoxy-based, or a hybrid.

How do fire protection intumescent paints work?

According to the FPA Australia, a substance with intumescent properties is characterised by the following:

  • When exposed to heat, the intumescent swells. When this happens, the coating decreases in density but increases in volume, making it thicker than its original state.

  • The chemical reaction balloons the intumescent paint into a chunky, foamy char which then provides  defense from high temperatures and fire.

It is important to emphasise here that intumescents are only capable of delaying the spread of fire or heat at specific times, not controlling the flames. They are graded according to fire ratings of 30, 60, 90, and 120 minutes.

How does the char form?

Ok, so we know that as a result of chemical reaction with heat, the intumescent paint thickens into a char that protects the steel within it. You might be asking, how does that actually happen?

Well, it (unsurprisingly) involves a chemical reaction. From a scientific point of view it can be explained like this.
When the temperature elevates to at least 250 degrees Celsius, ammonium polyphosphate decomposes into phosphoric acid, signaling the start of the process of charring. The acid then reacts with pentaerythritol, forming polyphosphoric acid esters that later on, form a foamable carbon matrix as a result of decomposition.

Ammonia and nitrogen then separate from the melamine, thus forming a stable, thermally-insulating char. At this stage, carbon slowly and continuously burns out based on phosphorous and titanium oxides, thereby protecting the steelwork from the extremely high temperature. 
 

How much intumescent paint fire protection system should you coat structural steel?

 
To know how much intumescent is needed for steelwork, you have to identify the size of the steel and the area exposed to fire. It is important for you to calculate the heating rate of the steel section based on the perimeter of the steel exposed to flames (Hp) divided by the cross-sectional area of the section (A).

When you have a high Hp and low A structural steel, it is mostly likely that that steel section is fast heating. This means that you need to cover this area with a thicker coat of intumescent paint to protect it from fire.  On the other hand, a low Hp and high A figure means that the section is considered to be low heating, thus a thinner coat of intumescent will suffice.

However, industry standards recommend a minimum of 0.2 mm coating to slow down the spread of fire by 30 minutes; up to 5 mm for 120 minutes.

As an aside, if this all sounds like hard work, or you are not sure if you are getting the optimal levels correct, we have a team of engineers with extensive experience in design optimisation, helping you to find the balance steel requirements,  concrete and product thickness and thus minimise the costs.

Which intumescent type is better?

To find out what works best for your construction needs and budget, let’s lay down the advantages and disadvantages of the four different types of intumescent technologies available in the market today. 

Solvent-based intumescent

 This was quite popular in the 1980s. Solvent-based intumescents usually contain hydrocarbons and are heavily loaded with chemicals. As a result they have high VOC levels, making the use of them significantly more dangerous compared to other intumescent types.
 
Coating and drying usually takes 8 hours and you will need to apply several coatings to achieve the requisite protection to ensure you protect the steel from fire.
 
The application of solvent-based intumescent is advantageous in semi-exposed environments.
 

Water-based intumescent

 
This is considered to be one of the safest intumescent technologies because it doesn’t have the toxic odour associated with the use of other chemicals. It has very low VOC, making it a more environmentally friendly choice in the industry. It is more ideally used on internal steelwork.

Unlike solvent-based intumescents, water-based fireproof paint is faster to apply and dry. In our range, we have the SC800 systems that provide up to 120 minutes of fire protection.
 

Epoxy-based intumescent

Designed for off-site use, this is a low-VOC intumescent that is considered to be a fast-cure system. It is durable and tough and  shows resistance to weather and rusting in as early as 1 hour after application.
 

Hybrid intumescent

The hybrid intumescent is the fastest drying fireproof coating among the group. It is also the most flexible because it can be used for both on-site and off-site applications and for internal and external structural steel.
 
It is almost hazard-free allowing trades to work alongside the applicator, thus meaning you can schedule more work to be done..

Nullifire has the world's only 'Hybrid' intumescent coating system

We are fortunate that at Permax, we have secured the Australasian licence to distribute the world’s only hybrid intumescent coating system, Nullifire SC902 that provides up to 120 minutes of fire rating protection.
It is a low-VOC coating that can be coated on internal and external structural steel. It can also be applied offsite and on-site, giving workers the flexibility required in construction work.

Another notable feature of SC902 is its ability to cure extremely fast even in low temperatures. It can dry within one hour of application, even in conditions where the temperature is zero degrees Celsius. It is also non-carcinogenic, based on the harmonized classifications under Annex VI of Regulation (EC) No. 1272/2008 (“CLP Regulation”).

The SC902 system is approved to be used in internal conditions (Type Z2), internal conditions with high humidity (Type Z1), internal and semi-exposed conditions (Type Y), and all conditions, including external (Type X). 

To learn more about SC902 and other intumescent paint systems from Nullifire, you should speak to our experts at Permax.

 

This entry was tagged : Char, Comparisons, SC801, SC902

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