Smoke Damage >> How To Remove Soot Stains From Stucco

In a final report in the series of non-thermal damage experiments, SNL reports on previously unpublished results including tests of conformal coatings, digital throughput, memory chips, hard disk drives, and electrical properties of fire smoke [19].2.1.7.1 Conformal Coatings In order to gauge the ability of conformal coatings to mitigate the effects of smoke exposure, a battery of high smoke load (200 g/m2) exposure tests were performed on functional boards with a variety of How To Remove Soot Stains From Stucco conformal polymer coatings (listed in Table 5, below) [19]. 

The circuits tested were the previously discussed HVLC, HCLV, HSD, HFTL and HFLPF constructed from PTH and SMT components. There were variations in response with different coating chemistries and electrical components, but in general, How To Remove Soot Stains From Stucco coated boards were less susceptible to damage than bare boards. 

When constructed from PTH components, the HVLC circuit maintained its resistance best with parylene or polyurethane coatings and How To Remove Soot Stains From Stucco varied the most (excepting the bare board) with the silicone coating. The SMT components maintained resistance well with parylene, polyurethane and acrylic coatings. Although the expected and most commonly observed degradation mode in the HVLC circuit was a loss of resistance, some PTH components showed increases in resistance during the burn phase of testing. 

It should also be noted that the epoxy coated SMT board did not recover appreciably after smoke was vented from the chamber, a behavior which was not observed in any other configurations (including bare boards).In the HCLV tests, How To Remove Soot Stains From Stucco only the bare SMT board showed a noticeable change. After the burn began,the resistance of the circuit rose from 1.46 Ω to 1.49 Ω. 

Resistance continued to increase slowly until the chamber was vented, at which point it remained constant. The bare SMT board showed no signs of recovery. With such a small change in resistance, How To Remove Soot Stains From Stucco it is not clear that this is a significant result. The HSD was protected very well by all conformal coatings. Of the 18 bare boards (9 SMT and9 PTH), 7 PTH boards and one SMT board experienced momentary transmission failures at some time after testing. 

Also, post test measurements showed that fall time response on the bare PTH increased from 1.6 ns to 2.2 ns, while SMT and How To Remove Soot Stains From Stucco all coated boards remained unchanged. As observed in previous tests, the bare transmission line circuits showed increased forward coupling at 50 MHz and decreased forward coupling at 500 MHz and 1 GHz while smoke was present. 

Coated boards showed no coupling response to smoke.The bare HFLPF circuits were mildly affected by smoke exposure, How To Remove Soot Stains From Stucco while coated boards showed almost no response.2.1.7.2 Digital Through put Smoke exposure tests were performed with a variety of fuels to determine the impact of smoke exposure on digital cable connectors [19]. 

A circuit board with linked pairs of D-sub miniature 9-pin (DB-9), D-sub miniature 25-pin (DB-25) and How To Remove Soot Stains From Stucco network modular (RJ-45) connectors was placed in the exposure chamber. Digital signals from a personal computer outside of the chamber were routed through this board in order to determine the impact of smoke upon these connectors. 

PVC, Douglas fir and jet fuel were used as fuels for these tests, rather than the standard cable mixture.DB-9, DB-25 and RJ-45 connectors were tested simultaneously in 19 tests and How To Remove Soot Stains From Stucco showed no signs of failure. Subsequent tests performed by intentionally bridging signal lines with a variable resistance indicate that conductance between pins on a connector must closely approach the conductance of the cables themselves before there is a significant risk of failure.2.1.7.3 

Memory Chips Smoke exposure tests were performed on memory chips to determine functionality and How To Remove Soot Stains From Stucco attempt to isolate physical parameters that can predict chip failure [19]. The standard exposure method and fuel mixture were used, with additional electrical testing continuing for one hour after venting the chamber. 

Smoke loads of 30 g/m3, 35 g/m3, 50-60 g/m3, and How To Remove Soot Stains From Stucco 150 g/m3were used.The five types tested were 3.3 V volatile Static Random-Access Memory (SRAM), 5 V volatile SRAM, DIP Erasable Programmable Read-Only Memory (EPROM), plastic-leadless chip carrier(PLCC) EPROM and 5V non-volatile SRAM.

Functional testing of the chip consisted of repeatedly writing data to the chips and reading it back. The response time of the chips and How To Remove Soot Stains From Stucco the error rate of read/write operations were recorded.The parametric measurements monitored leakage current behavior. 

The current drawn when the chip was powered but not operating, current when a standard voltage is applied to a given pin and How To Remove Soot Stains From Stucco the voltage required to maintain a particular current were measured repeatedly at 30 s intervals. The exposure tests for electronic memory determined both functionality and the electrical parameters (voltage, current etc.) of the chips during and after smoke exposure. 

Functionality was determined by the ability of the chip to be accurately written to and read from. Table 6 indicates success and failure rates. The non-volatile SRAM suffered no failures even at higher (150 g/m3) fuel loads. Comparison of failures to the parametric data showed no consistent correlation between leakage current and How To Remove Soot Stains From Stucco failure. 

When the 3.3 V SRAM chips failed, How To Remove Soot Stains From Stucco their operating current roughly doubled,while the operating current of the 5 V SRAM dropped to half of normal during failure. Although some of the recorded failures occurred shortly after the smoke chamber vented, all chips functioned properly when tested several weeks later, indicating recovery after exposure.2.1.7.4 

Hard Disk Drives Hard disk drives (HDD) isolated from other computer components were tested for read/write functionality during and after exposure and How To Remove Soot Stains From Stucco were scanned for corrupted data sites after exposure[19]. Five drives were tested six times. In the first test the drives were oriented as they would be in normal use. 

In all subsequent tests, How To Remove Soot Stains From Stucco the drives were inverted to increase soot deposition onto exposed circuit boards on the underside of the drives. The standard smoke exposure method was used with fuel loads of 15 g and 30 g. In two of the tests, the nitrogen purge protecting the optics was deactivated, to prevent the dry nitrogen from lowering the humidity of the chamber. 

All drives passed the in situ functionality tests. One of the 5 disks showed signs of corrupted data,but the cause was not identified.2.1.7.5 Electrical Measurements Two important electrical properties of smoke are conductivity in the gas phase and How To Remove Soot Stains From Stucco conductivity on surfaces. Surface conductivity measurements were performed with the previously described interdigitated comb and a specialized low-mass comb board. 

Gas conductivity was measured with pairs of freestanding, parallel perforated stainless steel plates. Masses of fuel between 1.5 g and 19 g were used.The comb patterns were biased with 5 V, 50 V and 500 V during exposure. Current flow was measured continually during and How To Remove Soot Stains From Stucco after exposure. The boards were weighted and visually inspected after exposure, to identify the mass and physical distribution of the deposited smoke.

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