CHAR 21
Protection from fire of steel and concrete structures

Since many years IRIS Vernici is involved in the development of intumescent
products technology and is marketing fire protection products in several
countries.

Six Italia, the company of the group specialized in application of protective
products, since 1994 is the italian marketplace leader for the fire protection of
train carriages and shipbuilding with the products developed and manufactured
in our facility in Basaluzzo, certified according ISO 9001:2000.

At the beginning of 2002 IRIS Vernici was the first company in Italy and one of
the first in Europe to enter the building marketplace with intumescent paints for
fire protection of steel certified according to the new and demanding European
Standard ENV 13381-4.

For the fire protection of concrete systems (separation walls, reinforced concrete
and pre-stressed reinforced concrete structures) IRIS Vernici offers a design
service based on results of numerous fire tests performed at official Italian
laboratories and finite elements modeling techniques to calculate the amount
of paint needed for each particular structure element and fire resistance
specification.

INTUMESCENT PAINTS

Among other materials for fire protection, intumescent paints offer some
unique features. In fact, they require a small amount of material per square
meter, allow simple application in thin films with high performance and can be
applied to architectural structures without changing their shape and appearance.

Moreover they have a very low environmental impact, especially when they are
based on new VOC-free technology, as is the case for our CHAR 21 and
           , certified for their ecological features by the Chemistry Department
of Cà Foscari University of Venice .

 

Char buildup of CHAR 21 after a fire test

However the use of intumescent paints for the protection of structures (of steel,
reinforced concrete or prestressed reinforced concrete) guarantees the
requested fire performance only if based on precise calculations to assess the
dry film thickness or the amount per square meter to apply as a function of the
structure to protect (type, thick or thin loadbearing elements, load on each
element, fire conditions, resistance specifications).

These calculations must be based on a proper series of experimental data
obtained on appropriate fire tests run in large scale in furnaces complying with
accurate standards.

Steel structures

Performance in the event of fire is given by the time it takes for the beam or
column to collapse. Actually collapse occurs because steel loose its loadbering
capacity almost completely for temperatures in excess of 500-600 °C. The time
to collapse, i.e., the fire resistance R expressed in minutes, for a protected
steel element depends on the paint dry film thickness, on the ratio between the
surface exposed to fire of the element and the related section area (mass
factor) and on the load on the element.
The fire testing in real scale of each
possible profile used in building construction would be excessively expensive
and time consuming, therefore a general fire test is performed on a series of
profiles having different mass factor coated with different amounts of paint.
The latest among these standard test methods issued worldwide, and according
to several experts one of the most severe, is the new european standard ENV
13381-4, used for the certification of CHAR 21.
Data obtained from this test are then analyzed with interpolation methods,
analytical mathematical methods or numerical models to obtain tables and
diagrams that are used by the engineer to calculate the thickness of paint
needed for each type of beam or column to obtain the desired resistance time.

For CHAR 21 IRIS Vernici supplies tables based on the critical temperature of
the structural element (must be estimated by the engineer depending on the
element load and according to building codes like, e.g., the Eurocodes or UNI
9502), the mass factor (obtained by handbooks or calculated geometrically for
the profile) and the requested resistance time R .

Alternatively we can supply the design guide specifically developed for IRIS
Vernici by FSD, using which the thickness to apply can be directly determined as
a function of load in the case of fire according to the Eurocodes .

Concrete and reinforced concrete structures

Due to the many possible shapes and size and reinforcing bars positions of the
possible structures built in concrete, bricks, reinforced concrete and pre-stressed
reinforced concrete, it is not possible to obtain calculation methods that are
simple and reliable as in the case of steel.

In this case the proposal of IRIS Vernici is to use its database of fire resistance
data of concrete structures, obtained by testing at the major Italian fire testing
institutes, as a base for calculation of the resistance of the elements actually
found in the structure being designed. The complexity of this problem makes a
simple analitycal calculation generally impossible and suggests to use finite
elements mathematical models to describe the temperature field inside the
element in the event of fire and consequently predict the resistance time.

Our models have been previously fine-tuned by numerical simulation of our
experimental tests and evaluation of the effective thermal conductivity of our
products. Therefore in a very short timeframe it is possible to calculate the
thickness of the intumescent protection needed for our customer's specific
problem.

An example, a reinforced concrete floor slab, is reported in the following picture.

Technical notes

Intumescence means "to swell up" and intumescent coatings are formulated
including several active compounds that react as temperature increases to form
a char and to evolve inert gases. The evolved gases cause the coating to
bubble, foam and ultimately expand up to 100 times its original volume as a
solid charred material. This material forms an insulating barrier which protects
the substrate from rapid increase in temperature. Such a protection is useful for
increasing time to collapse under fire for steel structures or to upgrade fire
resistance of walls or ceilings of various materials.

Intumescent paints suffer from poor resistance to weathering. For this reasons
the product must be protected with a waterproof topcoat when used outdoors or
in moist environments.
Maximum protection is achieved with 2 component polyurethane systems, such
as our PURETHAN . Chlorinated rubber paints can also be used, such our
CLORIDROX , which also partly contribute to the reaction-to-fire performance.
In the case of slight humidity, for a temporary protection or simply to refinish
the work with a pleasant colour, acrylic waterbornes can be used, such as our
IDROSOL .
Also occasional exposure to rain before applying the topcoat should be
avoided.

Performance during fire of the whole system may be affected by the thickness
and type of primer and topcoat. According to some norms, a fire test should be
performed of the primer-intumescent-topcoat system to check compatibility.
IRIS Vernici has data available from fire tests of its primers and topcoats and
of several others from the market.

A suitable anticorrosion primer should be previously applied to protect steel
from corrosion (the intumescent coating is not effective to this purpose) and to
provide adhesion. Many primers on the market are suitable and do not
adversely affect fire performance. This is generally true for those primers that
cure by crosslinking or oxidative reticulation, like, e.g., 2K epoxies or long oil
alkyds. Primers with thermoplastic binders, like bitumen, chlorinated rubbers or
physically drying acrylics are NOT generally suitable. However a prior
experimental test or the advice of our technical service is always recommended.

Smoke emission from intumescent coatings is generally low, both with respect
to smoke optical density and toxicity. However some care should be taken,
when required by specific regulations, to the possible formation of thermal
decomposition by-products, also considering the topcoat (e.g. PUR may raise
concern for HCN or fluorinated coatings for HF).

Hardness and aspect of an intumescent paint are similar to those of a latex
paint, but thickness is as high as one or two millimeters. Therefore scratches
can occur after painting, especially when steel beams are pre-coated in a paint
shop. To ensure proper function of the coating, scratches must be properly
repaired with an intumescent putty ( CHAR TIXO ).
The problem of poor weathering is reduced in intumescent epoxy coatings
( CHAR 27 ) that are designed for use in harsh environment. They give a lower
expansion ratio and a thougher char.

The same problem is fully overcome with special paints, like CHAR 23 and
CHAR 24 , that show a great weathering resistance without any topcoat. Their
fire performance, however, make them suitable at the moment only for specific
applications with short resistance time requirements.

Other materials based on the same technology, the products of the IRISEAL
series, are particularly useful as intumescent sealers for joints and cables
penetrations . They are supplied both in drums or cartridges.

CERTIFICATES, TEST AND ASSESSMENT REPORTS

CHAR 21: Test report n° Pr-04-01-02.093 of 03.01.2002, Pavus Institute,
Prague , Czech Republic

CHAR 21: Assessment report n° PKO-02-1.027 of 19.09.2002, Pavus Institute,
Prague , Czech Republic

CHAR 21: Assessment report "Char 21 fire retardant paint on steel structures -
Design guide based on prENV 13381-4”, FSD Fire Safety Design AB, Malmö,
Sweden, 06.08.2002

CHAR 21: Test report on compatibility of primers and topcoats, J. Seidl & spol.
s.r.o., Dvur Kralove , Czech Republic . Tests performed at PAVUS testing station
in Veseli nad Luznici , Czech Republic , May 2002

CHAR 21: Certificate by the Chemistry department of the University of Venice,
Italy, on the “Ecological assessment of the product CHAR 21”, 20.03.2002

   : Test report CSI 0992 RF of 31.01.2001 - REI 120, Istituto CSI,
Bollate , Italy

   : Test report CSI 0981 RF of 07.01.2002 - REI 90, Istituto CSI,
Bollate , Italy

   : report 176163 of 07/10/2003, Istituto Giordano, Bellaria, Italy