Elsevier

Fire Safety Journal

Volume 61, October 2013, Pages 92-99
Fire Safety Journal

Development of smoke corrosion and leakage current damage functions

https://doi.org/10.1016/j.firesaf.2013.08.016Get rights and content

Highlights

  • Smoke damage functions developed for materials used in semiconductor fabrication cleanrooms.

  • Leakage currents, normalized with smoke deposition, presented from combustion of PC, PVC & Nylon.

  • Corrosion rates, normalized with smoke deposition, presented from combustion of PC, PVC & Nylon.

  • Linear polarization & electrical resistance techniques used to evaluate smoke-induced corrosion.

  • Tube furnace apparatus developed for exposing sample targets to damaging smoke.

Abstract

Smoke damage functions have been developed for representative materials used in smoke sensitive facilities such as semiconductor fabrication cleanrooms or data centers. Leakage currents and corrosion rates, normalized with the total smoke deposition per unit surface area, are presented from the flaming combustion of polycarbonate, PVC and Nylon. When coupled with smoke deposition rates, these damage functions can be used to assess expected damage levels for specific fire scenarios.

Introduction

Smoke is a mixture of (1) particulates consisting of soot, semi-volatile organic compounds (SVOC), and solid inorganic compounds; and (2) non-particulates consisting of very volatile organic compounds, volatile organic compounds, and liquid and gaseous inorganic compounds. Soot creates bridging between electrical conductors and conveys corrosive products, resulting in damage to electronics and electrical circuits through leakage current and corrosion, while SVOC and non-particulates stain and impart malodor to surfaces. Soot is also a very effective adsorbent and transport mechanism for SVOC, non-particulates and inorganic compounds. Facilities such as those associated with semiconductor fabrication or data storage and processing are particularly sensitive to smoke damage created through soot deposition leading to leakage current and/or corrosion.

Leakage current between two conducting elements occurs as a result of circuit bridging due to the presence of a conducting medium between the elements, such as water, conductive ions, soot, or dust. The increase of leakage current on electronic circuit boards can change overall circuit characteristics, e.g., degrade and/or damage circuit properties. This principle has been used to design a leakage current target for the measurement of smoke corrosivity [1], [2], [3]. The target, as shown in Fig. 1, has a comb-like pattern made of thin strips of copper with 40 insulating spaces between them. The dimensions of the target are shown in the figure.

Specifically, for example, with respect to the manufacture of semiconductors, leakage current is uncontrolled (“parasitic”) current flowing across region(s) of semiconductor structure/device in which no current should be flowing. Leakage is one of the main factors limiting increased computer processor performance. The presence of ionic compounds and soot in smoke deposited on the surface of a semiconductor is expected to damage the processor's functionality through an increase in leakage current.

Corrosion involves the reaction between a metal or alloy and its environment. It is an irreversible interfacial reaction, which causes the gradual deterioration of metal surface by moisture and corrosive chemicals. In aqueous or humid environments, corrosion is an electrochemical reaction in nature; it involves electron (e) transfer between anodic and cathodic reaction sites. For corroding metals, the anodic reaction is the oxidation of a metal to its ionic state [4].

 M⇒Mn++neSpecific examples of anodic reactions:Cu⇒Cu2++2eAl⇒Al3++3eSn⇒Sn2++2eThe cathodic reaction is a reduction process. For metallic corrosion, cathodic reactions like Eqs. (5), (6), (7) are frequently encountered. In acid solutions, hydrogen evolution and oxygen reduction reactions (Eqs. (5), (6)) are the main cathodic reactions. In neutral or basic solutions, oxygen reduction reaction (Eq. (7)) is the primary cathodic reaction.

Hydrogen evolution2H++2e⇒H2(g)Oxygen reduction (acid solutions)O2+4H++4e⇒2H2OOxygen reduction (neutral or basic solutions)O2+2H2O+4e⇒4OHIn general, corrosion caused by smoke is due to the presence of inorganic anions in smoke such as chloride (Cl), bromide (Br), and fluoride (F) plus moisture in the environment. In fires, corrosive combustion products such as HCl, HBr and HF are emitted along with the other combustion products, which are present as gases, liquids and solids. The corrosive combustion products are generally emitted as gases and liquids from inorganic anions in the structure.

The non-corrosive combustion gases and liquids are emitted as inorganic and organic compounds and water, whereas solids are emitted as soot and inorganic metals and dust. The solid combustion products are broadly defined as particulates and the gaseous and liquid combustion products are broadly defined as non-particulates. The mixture of particulates and non-particulates that include products with inorganic atoms is defined as smoke.

The main hazards regarding the exposure of electrical/mechanical equipment to smoke is the damage due to circuit bridging, corrosion, and binding, defined as smoke corrosivity. Circuit bridging occurs in reducing surface insulation and increasing leakage current for digital safety systems, multiplexers and functional circuit boards. In contrast, corrosion damage by acids and anions from smoke can be observed either short term or long term after the fire. Smoke contamination also leads to other types of electrochemical corrosion degradation of circuit boards, such as dendrite metal migration between conduction lines, localized corrosion of uncoated metal wires and contacting areas, etc. Failure mechanisms and causes for electrical/mechanical equipment as a result of exposure to smoke are listed in Table 1 [5].

Section snippets

Experimental set-up

The following section describes the experimental setup that has been developed for making various types of smoke damage and combustion process measurements. There are two main measurement stations within this setup. The first is the Smoke Exposure Chamber (SEC) and the second is the U-tube measurement duct. Smoke generated by the tube furnace supplies one of either of these measurement stations, but not both simultaneously. Fig. 2 shows the schematic of the Tube Furnace System experimental

Background leakage current (unexposed)

Experimental data of background leakage current (LC) versus relative humidity (RH) for new and unexposed LC targets are shown in Fig. 5, where reference data from the IEC/TS 60695-5-3 [2] are also included. Error bars, as indicated in the figure, are typically comparable to the symbol size used to represent the data and therefore not uniformly discernible. As shown in the figure, the average LC increased from 1.1×10–11 A at 30% RH to 1.1×10−6 A at 90% RH due to the increase of conductivity with

Smoke corrosion

The linear polarization resistance (LPR) and electrical resistance techniques based on electrochemistry were used to evaluate smoke-induced corrosion on metals. The LPR technique enables the corrosion rate of metals in solution to be measured as in milli-inch per year (mpy). Fig. 13 shows the setup of a handheld LPR probe (model MS1500L, Metal Samples, Munford, Alabama USA) with its copper electrodes (UNS C11000). The corrosivity (or corrosion rate) of a bubbler solution collected after each

Summary discussion

Two potential smoke damage functions are identified for application to smoke sensitive facilities, such as semiconductor fabrication cleanrooms and data centers—one associated with leakage current (i.e., uncontrolled current flowing across region(s) of an electrical structure/device in which no current should be flowing) and the other due to surface corrosion. Table 5 summarizes the damage functions for polycarbonate, PVC and Nylon. As shown in the table, of the three representative materials

References (9)

  • T.J. Tanaka

    Measurements of the effects of smoke on active circuits

    Fire and Materials

    (1999)
  • IEC/TS 60695-5-3 Ed. 1, Fire Hazard Testing-Part 5.3: Corrosion Damage Effects of Fire Effluent-Leakage Current and...
  • R.P. Frankenthal et al.

    Accelerated life testing of electronic devices by atmospheric particles: why and how

    Journal of the Electrochemical Society

    (1993)
  • M.G. Fontana

    Corrosion Engineering

    (1986)
There are more references available in the full text version of this article.

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