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Control Systems – Fire Retardants as Applied on Site

The control system for fire retardant treatment for wood is done on site to ensure that the right amount of fire retardant treatment is applied so that the desired fire class can be achieved. Supplier of paint or liquid and certified providers are responsible for the control. Various control systems are necessary for film-forming and non-film forming fire retardants.


A. Test for fire retardant paints (film-forming)

Control and measurement is carried out on site and are based on the determination of the paint coats thickness on the wooden surface by drilling a small hole in the paint. The following steps are to be included in the control:

  1. The measurement should always be carried out in dry conditions. For the measurement an as flat as possible surface is to be preferred, such as on top of twigs and such as.
  2. All measurements should be carried out in accordance with ISO 2808, with a Coating Drill, and in accordance with ISO 19840: 2002, with adjustments for the measurements on wood.
  3. 3-5 holes are to be drilled per 10m2 of painted surface. In each hole, two measurements are to be carried out, preferably diametrically opposed, which in the easiest way possible increases the number of measurements and reduces sources of error.
  4. Large areas are to be divided into fields of roughly the equal size and all fields are to be measured so that the values ​​are an average of the total area.
  5. The measurements shall be recorded in both single and mean values.
  6. The report is to include information on the type of product, producer, painter, the date of painting and date of control measurements.
  7. The report is to be signed by the executives, and sent to the constructor, painter, producers' representative and NBT.
  8. If possible, attached photos of the measurement to the report.
  9. Acceptance Criteria: The following criteria in accordance with ISO 19840 must be met.
  • The arithmetic mean of all individual dry film thickness’s must be equal to or greater than the nominal dry film thickness’s (NDFT) to achieve the intended fire class;
  • All measured individual dry film thickness's must be at least 80% of NDFT.


B. Test for Fire Retardant Liquids (Non-Film Forming)

The control is carried out by sampling on site with subsequent testing in a laboratory. Two methods can be used:

a. Fire test on a small scale

Fire testing in accordance to ISO 5660 (cone calorimeter) is preferred. A minimum of three test pieces of a 100×100 mm are collected and spread evenly over the surface. The fire test is carried out in two tests at a radiation intensity of 50 kW/m2, the time to ignition, heat and smoke are measured and used to formulate the fire resistance classification.

b. Measurement of active substance

A samples of the surface layer about 3-5 mm deep is collected. At least ten samples with a diameter of 3-5 mm are collected and evenly distributed over the surface, see Method A. The samples are then to be analysed in regards to active substances for fire resistance and requires that the producer indicates amount of active ingredient to achieve the specified fire rating.

NBT works with SP Certification (formerly SITAC) to develop certification rules for personal certification of fire retardant painters. More information will be presented soon.

The article on the new control system have been published in the Bygg & Teknik 2 2012 (2012 06 Bygg och Teknik Kontrollsystem) and Brand posten # 48 2013 (2013 48 Brandposten Artikel SP Trä).