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ASFP – GUIDE BEWARE THE MIS-USE OF PU FOAMS WHEN FORMING FIRE SEALS
Many polyurethane (PU) foams claim to be “Fire Rated‟, often citing a Class B1 or similar performance when tested
to DIN 4102, or Class D when tested against European standards.
These classes, however, refer to “reaction to fire‟ classifications that are concerned with the ignitibility, surface flaming and heat release characteristics of the material and as such, can cause confusion.
“Reaction to fire‟ classifications cannot support the use of the material where fire resistance is required, such as in linear gap or service penetration seals and to help clarify the situation, the ASFP has published a simple Advisory Note (TCOM N15). The Note is designed to give advice on the general properties of such foams, in support of their correct and safe use in fire seal applications.
There are many PU foams currently available on the market. They are supplied in pressurised cans for hand held, or gun application. The foam is normally expelled as a sticky liquid, through long nozzles and quickly expands by, typically, 40 times its original volume, to form ridged finish.
PU foams that are to be used in linear gap, or service penetration applications, must have their fire performance determined by testing to the appropriate national, or European fire resistance test Standards. In the UK the appropriate Standard is BS 476: Parts 20/22 (BS EN 1366-4 in the case of linear gaps) and BS EN 1366-3 for service penetration seals. Once tested to the required Standard(s) it is important that the scope of application of the test results is assessed by a competent person, or organisation, in accordance with current industry agreed guidance and that the product is not used outside of the scope of such guidance without further support from expert opinion.
When CE marking of penetration and linear gap seals begins, extending the scope of application will be undertaken using Extended Application Standards, rather than assessments. CE marking is expected to be mandatory in 2013 when the Construction Products Regulation replaces the Construction Products Directive.
GUIDE on – Dielectric constant/material of the data cabling.
A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. Dielectric materials are used in the construction of radio-frequency transmission lines as balanced lines or waveguides are dependent on characteristic impedance. In essence, an electric field must exist for their operation but must not break down and conduct electricity.
DC or low frequency line transmission is concerned with the resistance or impedance of the conductor as the signal is conducted. The concerns for materials covering a conductor are aimed at insulation properties only i.e. at what level of power will the material start to conduct or break down (dielectric breakdown).
However, radio-frequency fields, such as those seen in structured wiring, are not as much reliant on the impedance of the conductor as the signal energy exists as a balanced electric field. In these scenarios the dielectric properties of the material are critical to it’s operation and the signal will have been lost way before dielectric breakdown. Due to this, when the dielectric constant is changed it can drastically effect the impedance value of the cable over the 100hms limit (±15). This will cause the cable to fail.
Chemical ingress can change the dielectric constant of a cable thus causing a change in the impedance value and causing failures in data transmission. However the change in the dielectric constant may not show up immediately but could occur in a longer time frame. This can be due to the hydroscopic nature of PVC and LSZH cable which can cause a capillary action of the Chemical within the cable.
GUIDE One Component Fire Rated Foams
Although many cans will state “up to 4 hours fire integrity” this will generally have been in tested in a very restricted environment.
This usually consists of an opening 15mm in diameter and 220mm deep. The lack of available oxygen in such a small hole mean that the flame cannot be sustained and the test will achieve 4 hours.
When the size of the opening is increased and a more realistic 100mm depth is tested, this may burn through in under 10 minutes.
The products are rarely tested around services and do not exert pressure in a fire so should never be used around plastic components or PVC etc.
Hilti and Globals recommendation is that single component PU foams should only be used as a backing material for a tested fire stop product.