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Tuesday, 30 October 2007 09:51

The First 24 Hours Post-Disaster

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Despite all reasonable precautions, a disaster has occurred. It could be a flood, lightning strike, fire or act of sabotage such as orange juice in the computer. The actions you and your insured take in the following 24 hours are critical in preventing irreparable damage, so that the affected equipment may be restored to pre-incident conditions. This degree of restoration is possible far more often than one may expect and in situations that, at first glance, appear hopeless.

Corrosion processes begin immediately following a disaster, but corrosion does not proceed at a uniform rate over time. The rate is greatest at or about the time when the fire is extinguished or the flood water has drained. Thereafter, the corrosion rate decreases gradually over time but never reaches zero.

Fire and Halogens

When dealing with fire aftermath, one must consider the effect of chloride ion in ferrous metal corrosion. This ion is almost always present because of the near universal presence of Poly Vinyl Chloride (PVC) electrical insulation, water piping and other articles. PVC is the most commonly used plastic in the world. However, when heated to over 200 degree Celsius, it decomposes with release of hydrogen chloride gas (HCI). Combined with the water that is either produced by combustion or otherwise present, hydrochloric acid (also known industrially as muriatic acid—one of the most corrosive chemicals known) is formed.

Another point to be considered is the usage of halocarbons in fire-extinguishing systems-known commercially as Halons (trademark of E.I. du Pont de Nemours & Co.) The two Halons used for this purpose are CF3, Br, Halon 1301 or BTM and CF2, CI Br, Halon 1211 or BCF. These materials are highly effective in halting combustion, even at low, nontoxic concentrations. For environmental reasons, the use of Halons is being discouraged, and fewer new systems are being installed, despite the fact that there are no good alternatives to them. Of course, we must deal with the thousands of Halon systems presently installed and in service. Halon 1211 will produce HCI. Both Halons will produce HBr and Br2, (hydrobromic acid and elemental Bromine), upon contact with flame or hot metal. These bromine-containing species are even more active than HCI in promoting the corrosion of ferrous metal. They also will attack copper, brass, zinc, aluminum and even the noble (gold, platinum, etc.) metals.

At the conclusion of the fire-fighting effort, conditions are optimum for rapid corrosion: hot, wet, acidic and highly halogenated. It is not entirely surprising to see moist brown rust appearing on steel surfaces even before the firemen have left the building. Fortunately, this rapid corrosion rate is not maintained for long. The temperature will drop, and ventilation will produce airflow that removes humidity and most of the acidic halogen gases. Within a few hours of the fire, it would be difficult to detect any HCI or HBr in the air. On surfaces inside the building, however, they remain easy to detect in puddles of water on the floor, inside equipment, in brick, concrete, fabric, dust, soot and other materials.

The corrosion processes are slow but continuous and progressive. Hydrochloric acid, which has been trapped in the above reservoirs, will gradually move back into the atmosphere. Being gaseous, it moves with the air currents and condenses on cold and moist surfaces. Equipment not initially affected by the fire will show signs of corrosive attack, even in distant areas of the plant building.

The initial attack of HCI or HBr upon a metal produces the metal halide salts. However, these are not stable when in contact with moisture, They will hydrolyze, or react with water in air of greater than around 50 percent relative humidity.

The Vicious Cycle

The hydrolysis products are basic salts, oxides and hydroxides of the metal. Further reaction may occur with oxygen from the air to produce rust (FeO.OH) on iron or steel. These processes may be written:

Fe + 2HCI > FeCI2, + H2, (gas) (1)
Fe CI2, + 2H2O > Fe(OH)2, + 2HCI (2)
4Fe(OH)2 + 02 > 4FeO.OH + 2H2O (3)

Note that the first two steps constitute a catalytic cycle, with the HCI being re-released, so as to cause rusting of more metal. This attack may occur all at a given place, or the HCI may be carried by air transport to other locations.

It may be worse if the attack proceeds in one spot, because this leads to pitting. When a slight surface depression forms, the oxides or hydroxides produced at the top of the depression are somewhat protective against further attack by HCI, so that the bottom of the depression corrodes more rapidly than the top. Because tiny oxidation-type concentration cells are set up, dissolution of iron is more rapid in regions of lower oxygen concentration than in higher ones. Reaction (3) is favored in the oxygen-rich upper areas that become cathodic with respect to the oxygen-poor lower areas where anodic dissolution, represented by equation (1), occurs.

Iron dissolves at the bottom of a pit and deposits as rust at the top. This process does not require the presence of chloride ion and would continue even if natural diffusion/ventilation processes removed all chloride contamination. Of course, total removal would require infinite time.

In the days following a disaster, corrosion produces its most damaging effects. Sliding surfaces become roughened and bearings lose essential smoothness. Chloride ion migrates to areas previously uncontaminated.

Bacteria and fungi will produce corrosion even on stainless steels and copper/nickel alloys, as well as cast iron, aluminum, and concrete. The sulfate reducing bacteria, such as Desulfovibrio, are supported by sulfate ion, which is produced in fires involving coal, paper, wood or heating oil. Furthermore, electrolytic corrosion occurs whenever two dissimilar metals are in contact with an external electrically conductive liquid. This can cause rapid failure of soldered, brazed or welded joints.

Electrical and Electronic Equipment

Special problems arise in regard to electrical and electronic equipment. Corrosion may attack the copper or solder tracks on printed circuit boards. Even gold-plated contacts are attacked. The usual thickness of gold plating is about six microinches (0.14 micron). Although large compared to the diameter of a gold atom, this thickness is not sufficient to provide 100 percent surface coverage. There are many holes in the plating. Electron microscopy shows that substrate corrosion product erupts like mushrooms through these holes. This product can interfere with electrical contact as soon as the components are moved, especially in low-voltage circuits such as those in computers or telephone exchanges.

When electrical machinery is allowed to continue operating subsequent to a contamination event, the large voltages involved produce major electrochemical attack on metal surfaces. In addition, the electrolytic conduction process will cause chloride ion to migrate into crevices and regions to which it otherwise would not penetrate.
Clearly, corrosive damage as described above can reduce any equipment to a condition beyond economical repair. However, there is no need to allow this damage to occur!

Deceiving Appearances

When an observer arrives at the scene of devastation and sees the red-brown flash-rust coating that arises during the first few hours, he or she may feel that the only option is to replace the equipment. This is a costly option. It involves the direct replacement cost plus the delivery time of new equipment. However, the flash-rust is essentially superficial. The underlying metal is still smooth because pitting has hardly begun.

If the equipment is sprayed promptly with a water-displacing protective oil, the corrosion may be effectively halted for a period of about a week in outdoor storage or two weeks indoors. During this period, a decision may be reached as to whether to restore the equipment.

Full restoration will involve disassembly as needed, removal of contamination, rust removal, re-oiling, reassembly and testing. Competent restoration companies can perform these procedures, in this country and abroad.

For best results, your chosen restoration company should be contacted and asked to perform the initial inspection and protective spraying within the 24 to 48 hours following a disaster. The cost is small and it buys valuable time. When this procedure is not followed, the results may be distressing..

Tales From The Crypt

A One-Month Delay. An electrical fire occurred in a basement area of an office building, exposing graphic arts printing equipment to smoke and corrosive vapors. Four weeks later, our engineers were called and performed an initial inspection. High chloride levels were found on metal surfaces, accompanied by much visible rusting. Chloride levels were lower on nonmetallic surfaces, due to natural processes of dissipation. While some of the affected equipment was restorable, other items were beyond economical repair. Had we been called earlier, all of this costly equipment could have been cleaned and returned to service. Instead, the operator was obliged to use the services of other printers in order to satisfy the needs of his clients.

Another One-Month Procrastination. Optical equipment was exposed to rainwater during transport on a flatbed trailer. The equipment was delivered in a wet and already corroding condition. The purchaser had reason to believe that the equipment was unusable. When our engineers performed an inspection five weeks later, they found that the damage was mostly cosmetic in nature, with some pitting in noncritical areas. The equipment was found to be readily restorable. If it had been dried and oiled when first received, virtually all the corrosion could have been prevented.

A One-Year Hesitation. An Automated Teller Machine (ATM) was dropped from the back of a truck, falling a distance of approximately 30 inches. Subsequently, it was allowed to sit outside the purchaser’s facility, exposed to the elements. Almost a year later, we were asked to send our engineers to perform a survey and inspection. Despite the severe initial damage, the machine had considerable salvage value—at the time of the accident. As a result of a year’s corrosion, that value was reduced to nil.

A Costly Mistake

During a school holiday period, a steam pipe ruptured in a local high school. This filled the music room with a high-temperature fog which condensed on and within the electronic equipment housed therein. Although no chlorides were involved, pipe scale and water additives (corrosion inhibitors and anti flocculants) contacted the affected equipment.

About one month later, our office was contacted, and a consultant was dispatched. At that time, he observed a good deal of corrosion on unprotected metal surfaces. Most of this appeared to be flash-rust, with little pitting. Corrosion on printed circuit boards was, in some cases, fairly extensive.

As might be expected, the higher-valued pieces of equipment were damaged to a greater extent than the cheaper ones. Thus, although complete restoration was entirely possible, it was not considered to be cost-effective.
Had the equipment been dried and oiled (where appropriate) immediately following the incident, there would have been virtually no lasting damage. As it was, a loss of over $20,000 was taken.

Roger P. Gordon is the Manager of Research and Development for RELECTRONIC Service Corporation in Totowa, N.J.

Read 2528 times Last modified on Thursday, 11 October 2012 08:18

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