Smoke Damage >> How To Clean Smoke From Walls And Floors After Grease Fires

After the 1974 electronic system fire in Poitiers France, CNET developed what is considered the first modern test of corrosivity [70]. A number of other standards have since been developed that utilize a variety of fire and exposure models as well as several different methods of reporting results. They generally use the same principle for measuring corrosion, which is to use the relationship between the thickness of a conductor and How To Clean Smoke From Walls And Floors After Grease Fires its resistance. 

The principle for making this measurement will be given and How To Clean Smoke From Walls And Floors After Grease Fires analyzed later. A common element of all direct tests is a combustion source used to generate the effluent which is exposed to a test probe for a period of time. The test probe is then kept in a controlled environment (for typically 24 h) at a specified temperature and relative humidity. 

Test measurements usually look specifically at the loss of metal from the test probe. All the direct tests use the same general method to measure the loss of material due to corrosion.The resistance of a conductor is related to its physical dimensions by where R is resistance, How To Clean Smoke From Walls And Floors After Grease Fires is the resistivity of the material, l is the dimension in the direction of the current and A is the cross sectional area of the material. 

For a rectangular cross section, A = wh,where w is the width and h is the height. If the only exposed surface is the top of the conductor, How To Clean Smoke From Walls And Floors After Grease Fires then any change in resistance can be related to the amount of material that is removed by corrosion from the top resulting in an increase in resistance of the conductor.

Direct test methods are broken into two types, static and How To Clean Smoke From Walls And Floors After Grease Fires dynamic. Test methods of each type are described below. Static Methods Tests are referred to as static tests if all the fire effluent is captured and held during the test. Generally the effluent is captured in the exposure chamber with the target present from the beginning of the test. 

Capturing all the effluent allows for the target to be exposed for a set period of time that can be significantly longer than the burning time of the sample. Static tests also make it easier to control the ambient conditions of the test such as the temperature of the gas and How To Clean Smoke From Walls And Floors After Grease Fires setting the relative humidity of the test chamber. 

The test emulates electrical equipment in the upper layer of the room of fire origin. ISO 11907-2, Plastics -- Smoke generation -- How To Clean Smoke From Walls And Floors After Grease Fires Determination of the corrosivity of fire effluents -- Part 2: Static method CNET in France developed what is generally considered to be the first modern corrosion fire test. 

This test method How To Clean Smoke From Walls And Floors After Grease Fires has been standardized as ISO 11907-2. The basic principle of the test as the standard states is "combustion – condensation – corrosion” [71].The test chamber is a 20 L (0.7 ft3) tube with a diameter of about 300 mm (11.8 in). One end has a sample holder where approximately 600 mg of the test sample is ignited and burned. 

At other end, How To Clean Smoke From Walls And Floors After Grease Fires a water-cooled test target holder keeps the target 10 C below the chamber temperature to encourage condensation on the test target. The test target is made up of 36 conductor lines with dimensions of 52 mm (2 in) long by 0.3 mm (0.01 in) wide by 17 m thick on a laminated epoxy circuit board. 

The nominal resistance, pre-test, is 8.0   0.5 . The reported value for the test isthe percentage change of the resistance of the test target. An initial resistance Riis taken beforethe test, How To Clean Smoke From Walls And Floors After Grease Fires and at any time t, the resistance is again measured giving Rf. The values are pluggedinto the following equation, which corrects for variations in initial resistance, to give the test valueܴ 

The derivation of this equation is given by Bottin [72].Test chamber conditions are set to 50 ºC (122 ºF) and How To Clean Smoke From Walls And Floors After Grease Fires 65 % relative humidity with the water cooled test target set to 40 ºC (104 ºF). The test sample is put in an inert crucible in the sample holder with the heating wire at 800 ºC (1472 ºF) and kept at that temperature for 3 minutes. 

After 60 minutes from the time the sample is placed in the sample holder, How To Clean Smoke From Walls And Floors After Grease Fires the final reading of resistance is taken, and the test target is removed from the chamber.By using the percent change in the resistance as the reported value of the standard, the CNET test has a nonlinear relationship between the reported value and the amount of corrosion that occurs.

The CNET categories are at 10 %, 20 % and 30 % change in resistance. Using the above equation, How To Clean Smoke From Walls And Floors After Grease Fires it can be seen that a 10.0 % increase in resistance would mean only 9.1 % of the conductor had been lost to corrosion, a 20.0 % increase would indicate a removal of 16.7 % ofthe conductor and a 30.0 % increase would mean only 23.1 % of the material had been lost to corrosion. ASTM E05.21.71 (withdrawn)

A second static test underwent a significant amount of development in ASTM E05.20. However,after ASTM D5485 was approved, How To Clean Smoke From Walls And Floors After Grease Fires development on ASTM E05.21.71 was discontinued and the standard was withdrawn. Since a great deal of work was done in the development of publications and test data referencing the standard, it is important to describe the test method.

ASTM E05.21.71 starts with the "NIST tox box” as the exposure chamber, How To Clean Smoke From Walls And Floors After Grease Fires which has a volume of 200 L (7 ft3). It uses a cylindrical quartz combustion cell that is connected to the exposurechamber by a stainless steel lined flue. Exposure ports are used for probe instrumentation and an additional port is connected to a 49 L (1.7 ft3) plastic expansion bag for pressure relief.

Test sample sizes were not standardized, How To Clean Smoke From Walls And Floors After Grease Fires but the samples were intended to be small enough such that combustion would not be oxygen limited. Test probes were manufactured by RohrbackCosasco. The basic configuration was of two legs of copper. One leg is shielded from theeffluent and used as at the reference. The other leg is exposed and is the measurement leg.

The test procedure used by Kessel, et al. [73] to expose the test sample places the specimen holder in the furnace and How To Clean Smoke From Walls And Floors After Grease Fires the furnace and test chamber are sealed. The atmosphere in the chamber is brought to 60 % relative humidity, the furnace heaters are set to 50 kW/m2, and the spark igniter is turned on and left running for 15 minutes. 

After 15 minutes, How To Clean Smoke From Walls And Floors After Grease Fires the spark igniter is turned off and the flue to the test chamber closed. The test probe is then left in the test chamber for another 45 minutes. The probe is then removed from the test chamber and put into an environmental chamber with 75 % relative humidity for 24 hours.

Finally, How To Clean Smoke From Walls And Floors After Grease Fires put in to a secondenvironmental chamber with 35 % relative humidity for six days.Measurements are made every 2 minutes to 3 minutes during the first hour, after 24 hours in thefirst environmental chamber and after the six days in the second environmental chamber.

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