Introduction - The need for Fire Protection

Fires are a threat to life, safety and building integrity.

Fire can spread from one area of a building to another, rapidly engulfing areas that were not originally affected by the fire.

Building structures may be weakened by the effects of fire and may collapse preventing escape and leading to a greater loss of life.

The majority of countries have building codes or building regulations that control the way buildings are protected against the effects of fire.

Although these vary globally they will all have similar goals which are to prevent or minimise loss of life and potentially minimise the loss of the building asset.

The Need for Fire Protection

Other fire control systems, such as sprinklers etc. are common in buildings and are detailed within specific building regulations. This training unit does not cover these ‘active’ types of fire control.

This training module will concentrate only on the fire protection of steel structures in buildings using passive fire protection (PFP), specifically ‘thin film’ intumescent coatings.

Fire Protection of Steelwork

Steel is an excellent building material but it is weakened by fire and therefore needs to be protected.

In a typical building fire, the temperature can reach 1200°C (2200°F) and as this occurs the temperature of the steel that supports the structure will also increase.

In time, the steel will start to lose strength with the risk of collapse of the building.

In general, steel retains approximately 60% of its room temperature and yield strength, and 45% of its stiffness at a temperature of 550°C (1020°F) with strength and stiffness rapidly diminishing above 550°C (1020°F).

It is therefore important to protect steelwork in a building or structure against the thermal effects of fire.

Fire Protection of Steelwork

Unprotected steel exposed to a fire can reach very high temperatures in a short period of time.

The steel can twist and buckle in this heat and lead to the potential collapse of the building.

This photograph illustrates unprotected twisted and buckled steel after a fire.

Thin film intumescent coatings will protect this steel and may allow a fire crew time to save the building from collapse and rescue occupants.

Fire Protection of Steelwork

There are several different forms of steelwork fire protection including:

• Boarding systems such as plasterboard, vermiculite board, etc.
• Spray applied cementitious, mineral fibre or gypsum systems.
• Spray applied thin film intumescent coatings.

This training module will concentrate only on the fire protection of steel structures in buildings using passive fire protection (PFP), specifically ‘thin film’ intumescent coatings. Thin film intumescent coatings are typically applied by the protective coating applicator by traditional methods used for many other protective coatings.

What is a Thin Film Intumescent Coating?

• It is applied like an ordinary coating, however at a greater film thickness. The dry film thickness is typically less than 5000 microns (200 mils).
• In a fire situation, a series of chemical reactions swell the coating to provide an insulating layer.
• This insulating layer protects the steel substrate from the effect of a fire.

There are a number of suppliers who produce thin film intumescent coatings.

What Types of Buildings are Protected with Thin Film Intumescent Coatings?

Typical examples of structures and buildings that are protected with Thin film intumescent fire protection coatings include:

• Football stadiums
• Shopping centres/malls
• Office buildings
• Cinemas and museums
• General public buildings
• Multi-level/multi-occupancy buildings
• Airports
• Warehouses

Thin Film Intumescent Coatings

A globally recognized definition of an intumescent coating is:

"A coating that reacts to heat by swelling in a controlled manner to many times the original thickness to produce a carbonaceous char that acts as an insulating layer to protect the steel substrate from the effects of fire"

Intumescent coatings are filled with raw materials that react and swell (intumesce) in a fire (typically to more than 50 times the applied thickness), producing a high carbonaceous insulating char.

In a fire situation, a series of chemical reactions occur within the coating causing it to swell and provide an insulating layer of a carbon-based char that protects the steel from the thermal effect of the fire.

As a consequence, it takes longer for the steel to reach the temperature at which it weakens, delaying the potential collapse of the building and allowing extra time for people to evacuate.

Charred Thin Film Intumescent Coating

This is an example of a thin film intumescent coating that has been exposed to a hot flame for 5 minutes.

Traditional protective coatings would have decomposed after this period of time.

The technology for intumescent coatings has improved in recent years and coating application is very similar to traditional coatings.

These coatings will however only work if they are applied correctly and at the specified dry film thickness.

Thin Film Intumescent Coatings

Thin film intumescent coatings look similar to many other viscous industrial coatings and are spray applied to steelwork in a similar way but at a greater dry film thickness.

The thin film intumescent coatings applicator should be aware of the importance of intumescent fire protection coatings and the potential implications for life and safety in the event of poor workmanship in their application.

Cellulosic Fire

In building fires, the fuel source is often considered to be items such as wood and paper. These materials are cellulose based and hence such fires are often referred to as a "cellulosic fires".

When intumescent coatings for buildings are tested under controlled conditions in a furnace, the tests carried out are often referred to as "cellulosic fire tests".

Cellulosic Fire

Using defined standard fire heating curves and associated test methods at independent and accredited fire test laboratories allows for different fire protection products to be evaluated. This helps to ensure the products have the required fire performance but it is also essential that the material is applied correctly as instructed by the intumescent manufacturer. This illustration shows one of a number of standard fire test curves as detailed in ISO 834*

It is important to be aware that the above explanation is very basic and that there are other fire types (e.g. hydrocarbon), against which protection is required in other industries.

*ISO 834-1: Fire-resistance tests - Elements of building construction. General requirements. International Standards Organization

Fire Testing

Fire protection manufacturers usually submit their product data and testing results to independent fire test laboratories to generate third-party assessment and certification of the performance of the product. This usually includes factory control auditing.

Fire testing and certification of intumescent coating systems are usually carried out by an accredited fire test laboratory.

The fire protection manufacturer must have the appropriate testing certification to be able to sell fire protection products.

Thin film intumescent coatings are typically rated under UL 263 "Standard for Fire Tests of Building Construction and Materials"

Cellulosic Fire

The following table provides some basic information about the fundamentals of cellulosic fire and the impact on buildings and people.

This table details the fundamentals of cellulosic fire and details the fuel source, fire temperature rise, market area, asset impact, time for loss of structural strength and impact.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• Fire protection duration, e.g. 30, 60, 90 minutes, etc. – typically the time required to evacuate the building and may also include additional time to allow a margin of safety for firefighters.
• Based on the exact duration of the fire protection, the thickness of the intumescent coating can be determined by the supplier.
• The thin film intumescent applicator should know the specific dry film thicknesses which may be detailed in the contract drawings, specifications etc.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• The type of steel element to be protected i.e. column, beams, hollow sections, etc.
• New steel buildings may use a mixture of columns, beam etc. and this can result in a different dry film thickness for each location.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• The critical temperature that the steel must not exceed for the duration of the fire, e.g. 550°C (1020^oF).
• As previously discussed, 550°C (1020^oF) is the cut-off figure used in detailing intumescent fire protection. Above 550°C (1020^oF), the steel loses strength and stiffness quite rapidly.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• Location of the steel, e.g. internal or external and whether internal members will be exposed to the weather during building erection, etc.
• It is critical that the designer reviews the location of the steel after erection. Some steel members may be partially exposed such as roof sections.
• A different intumescent coating type may be required for external locations or areas of high humidity or dampness.
• The building program must consider the application of the intumescent coatings to ensure any site application of intumescent has controlled environments during application, cure and general exposure during construction.

Fire protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

Corrosivity (ISO 12944)

Engineers and Specifiers will generally review the environment prior to writing the coating specification.

Atmospheric environments are classified into six atmospheric – corrosivity categories:

• C1 Very low
• C2 Low
• C3 Medium
• C4 High
• C5-Very high
• CX-Extreme

The table gives examples of corrosivity C1-CX.

Corrosivity Table

Corrosivity Table (cont)

C4 to CX

ISO 12944 (Corrosivity)

ISO 12944 is a typical document which defines the corrosivity which must be considered when a coating or intumescent fire protection specification is being developed. Other similar documents may be used globally.

The coating manufacturer will recommend the coating and sealer coatings etc. to suit the environment.

If the environment is not considered at the design stage, failure could be the outcome!

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• The environment (corrosivity) to which the fire protection system is exposed. 
• Could the environment change in the future?
• Could the coating be subject to wear, tear or damage?
• Could the coating be subject to cleaning materials, splashes or fumes?

If any of the above is a possibility, then advice from the manufacturers must be sought.

Future maintenance must always be considered. 

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

Shop or site applied

• It is possible to apply thin film intumescent paints at a factory before the construction which will minimize the construction build and reduce cost, however, the right products must be chosen as the steel will be subject to transport movement, erection and potentially longer environmental exposure.
• The variation in drying and overcoating times of the intumescent coatings between suppliers becomes an important element when applying intumescent in a factory environment.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

Implications for the building program -

• The application of the intumescent coatings must be considered during the building program.
• Access, surface pre-cleaning, application of the intumescent coating, drying etc. must be carefully considered along with other trades who may be required.
• There are many examples where the intumescent application has a limited program time as it is sometimes considered as a ‘coating of paint’. This can result in application and product defects.

Shop Applied Thin Film Intumescent Coating

This video demonstrates the application of a thin film intumescent coating to structural steelwork in a paint shop.

It is important to get a warm environment with a good airflow to ensure the coating can dry before being stored or transported to the site.

The process is more efficient than site application, although the mechanical damage can be large unless the coating has enough time to dry and harden.

Two-part intumescent coatings are beneficial to this process.

New faster drying intumescent coatings are under development, however, this new technology may come at a higher material cost.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• The aesthetics of the finished product for the environment, i.e. what the finish will look like.
• It is vital that the designer considers what the thin film intumescent coating will look like when the coating has been applied. This information should be available pre-tender.
• A test piece should be considered at the start of the contract and agreed by all parties.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• The cost of the product selected.
• Intumescent coating suppliers will calculate the material costs based on the thickness requirements on the specific project.
• Based on the location of the product, a maintenance or lifetime cost may have to be considered also.

Fire Protection Design – Thin Film Intumescent Coatings

When determining the fire protection system for a building or structure the following are normally considered:

• Certification for the thin film intumescent product establishing its credentials to meet the project fire protection requirements.
• The designer will review the specific certification for the product to ensure it meets the criteria and requirements. This is not the duty of the applicator.

Fire Protection Design – Thin Film Intumescent Coatings

The applicator will normally be given drawings or other means of identification of the steel sections that need to have intumescent applied to them.

They will also be given the thickness to apply to the steelwork – this may be one thickness for all sections, or it may be a range of different thicknesses to be applied to different steel elements of the building.

The responsibility of the thin film intumescent coating supplier is to have some input on the film thickness and assisting with the calculation.

Ultimately it is the thin film intumescent coatings applicator to correctly apply the coatings to the specified dry film thickness.

Summary

Within this training unit, we discussed the basics of fire protection and why fire protection is used for the protection of steelwork.

We also discussed thin film Intumescent coatings and types of fire and fire protection design.