Smoke Damage >> How To Clean Soot Off Furniture

Tests of CO2 with or without smoke had no effect on the functionality of the circuits, but did drastically reduce the temperature of the environment. Overall, SNL concluded that important failure mechanisms included both long-term corrosion and short-term current leakage or circuit bridging, particularly on the typically uncoated edge connections and How To Clean Soot Off Furniture interfaces. 

Digital systems not directly exposed to fire were seen to be able tomaintain functionality for How To Clean Soot Off Furniture about one hour following exposure.2.1.5 Smoke Exposure and Circuit Bridging in Digital Equipment SNL conducted tests specifically to assess the likelihood and impact of circuit bridging in digitalcircuits exposed to smoke. 

Smoke exposure tests were performed on a group of components selected to be typical of modern microprocessor electronics at the time [6]. During the tests, How To Clean Soot Off Furniture the smoke exposure environments were altered to represent different fire scenarios. The size of the fuel package was varied to either 3 g or 100 g, and in some tests the standard fuel mixture was modified to include PVC insulated cables. 

Other prescribed deviations from the standard test procedure were applied in various tests. These modifications were How To Clean Soot Off Furniture reduction of the furnace heat flux to 25 kW/m2, reduction of the humidity to 20 % RH,application of compressed CO2 as a post burn suppression agent and inclusion of galvanizedsheet metal among the test components. 

The use of galvanized metal was prompted by reports , How To Clean Soot Off Furnitureon corrosion-related phenomena that can result in conductive liquids capable of damaging electronics [6].The first variety of test board had a pattern of copper traces forming four interdigitated combs.The theory of the test is that deposition of soot and other products of combustion would providea conductive path between the combs and reduce the overall resistance of the pattern. 

The initialresistance between the combs varied between 1x108Ω and 1x1015 Ω . During the smoke exposure, How To Clean Soot Off Furniture potentials of 0 V, 5 V, 50 V, and 160 V were applied to investigate the hypothesis that local electric fields could promote soot deposition. The results show the relative change inresistance after exposure.

The second test board measured resistances between adjacent leads on a variety of printed circuit board (PCB) mounted chip packages. These included four surface-mounted components and How To Clean Soot Off Furniture three through-hole-mounted components. The components represented a range of commongeometries using either plastic or ceramic packaging. 

The boards were energized to 5 V and actively monitored for resistivity changes during smoke exposure. In every test of the chip packages and the comb patterns, How To Clean Soot Off Furniture four test boards were used; one was kept outside of the exposure chamber as a reference, one was kept in a computer chassis inside the exposure chamber, one was sprayed with a protective acrylic coating and one was completely unprotected.

In addition to resistance measurements, the test boards, dual in-line package (DIP) opticalisolator chips and How To Clean Soot Off Furniture memory chips were tested for functionality. The optical isolators wereevaluated by measuring their ability to reproduce a supplied square wave signal, the amplitude,and the delay of response to inputs. 

The exact nature of tests performed on the memory chips after exposure is not specified, but rather expressed by pass/fail criteria. The most fundamental evaluation of circuit bridging in these How To Clean Soot Off Furniture tests were active resistance measurements of PCBs before, during and after fire exposure.It was observed that comb patterns held at higher voltages collected more soot than identical patterns with low or no voltage applied. 

Also, when large particles of soot struck the highest voltage patterns (160 Vdc) visible sparks were observed. There were no quantified data presented on this topic. Figure 2(a) shows the resistance before and How To Clean Soot Off Furniture during exposure for the 160 Vdc comb patterns. The line indicates no change in resistance so that points below it correspond to a decrease in resistance while points above correspond to an increase. 

Boards exposed to smoke (bare, coated and chassis-mounted) generally showed significant drops in resistance. Some sense of the consistency of the experiments can be seen in the results for the control boards, How To Clean Soot Off Furniture which ideally would have exhibited constant resistance but, in fact, increased in resistance. 

These results are representative of data from testing as a whole. Similar resistance changes occurred for lower voltage combs and How To Clean Soot Off Furniture for components mounted to the boards.Figure 2(b) presents comparable results for resistance during exposure and averaged over the first 22 hours following venting of the chamber. 

These data provide insight into the tendency of components to either recover from damage or How To Clean Soot Off Furniture suffer long term degradation. Components which initially maintained a relatively high resistance tended to recover slightly while those that showed large resistance losses during exposure continued to suffer damage after venting.

In order to determine the significance of test parameters, linear models were constructed topredict the resistance before, during and after exposure. Individual factors as well as combinations of two and three factors were expressed as binary values and How To Clean Soot Off Furniture assigned coefficientsby means of a least-squares regression analysis. 

Since insignificant factors (those having very small coefficients) were omitted, How To Clean Soot Off Furniture the frequency with which a factor or group of factors appears in these models is a strong indicator of the impact (either positive or negative) that it has on circuit bridging. The condition of the board (bare, coated or chassis mounted) and humidity level were seen to be the most influential individual factors. 

It is also clear that bare boards were very susceptible to a combination of high fuel load and high humidity; while chassis mounted boards were heavily influenced by the combination of high fuel load and How To Clean Soot Off Furniture the presence of galvanized metal in the test chamber. Although the presence of PVC in the fuel did not appear to be significant, the authors note that the basic cable did contain high concentrations of Cl and Br and may have had a similar impact on conductivity and corrosivity of gases.

In 4 of the 27 tests, the isolator stopped transmitting a signal entirely. In other tests, there were significant differences between input and How To Clean Soot Off Furniture output signals, which could adversely affect the function of systems that depend on those signals. The memory chips failed in 6 of the 27 tests.In all but one case, failures of these components occurred only when the previously discussed linear models predicted low resistance across the leads of DIPs.

These tests clearly demonstrate the potential of smoke deposition to cause failure of electronic systems by circuit bridging. The humidity and How To Clean Soot Off Furniture amount of fuel consumed both strongly contributed to the degree of bridging. Also, flaming rather than smoldering combustion was more likely to result in lowered resistance. Conformal coatings and mechanical enclosures were seen to provide a measure of protection from smoke.

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