Editing Smoke (section)

===Corrosion===
Smoke can contain a wide variety of chemicals, many of them aggressive in nature. Examples are [[hydrochloric acid]] and [[hydrobromic acid]], produced from [[halogen]]-containing [[plastic]]s and [[fire retardant]]s, [[hydrofluoric acid]] released by [[pyrolysis]] of [[fluorocarbon]] [[fire suppression agent]]s, [[sulfuric acid]] from burning of [[sulfur]]-containing materials, [[nitric acid]] from high-temperature fires where [[nitrous oxide]] gets formed, [[phosphoric acid]] and [[antimony]] compounds from P and Sb based fire retardants, and many others. Such [[corrosion]] is not significant for structural materials, but delicate structures, especially [[microelectronics]], are strongly affected. Corrosion of [[circuit board]] traces, penetration of aggressive chemicals through the casings of parts, and other effects can cause an immediate or gradual deterioration of parameters or even premature (and often delayed, as the corrosion can progress over long time) failure of equipment subjected to smoke. Many smoke components are also [[electrically conductive]]; deposition of a conductive layer on the circuits can cause [[crosstalk]]s and other deteriorations of the operating parameters or even cause short circuits and total failures. [[Electrical contact]]s can be affected by corrosion of surfaces, and by deposition of [[soot]] and other conductive particles or nonconductive layers on or across the contacts. Deposited particles may adversely affect the performance of [[optoelectronics]] by absorbing or scattering the light beams.{{citation needed|date=May 2021}}

Corrosivity of smoke produced by materials is characterized by the corrosion index (CI), defined as material loss rate (angstrom/minute) per amount of material gasified products (grams) per volume of air (m<sup>3</sup>). It is measured by exposing strips of metal to flow of combustion products in a test tunnel. Polymers containing halogen and [[hydrogen]] ([[polyvinyl chloride]], [[polyolefin]]s with halogenated additives, etc.) have the highest CI as the corrosive acids are formed directly with water produced by the combustion, polymers containing halogen only (e.g. [[polytetrafluoroethylene]]) have lower CI as the formation of acid is limited to reactions with airborne humidity, and halogen-free materials (polyolefins, [[wood]]) have the lowest CI.<ref name="physproppoly">{{cite book |last=Mark |first=James E. |url=https://books.google.com/books?id=fZl7q7UgEXkC&pg=PA909 |title=Physical properties of polymers handbook |publisher=Springer |year=2006 |isbn=978-0-387-31235-4 |access-date=25 September 2016 |archive-date=2 August 2020 |archive-url=https://web.archive.org/web/20200802054508/https://books.google.com/books?id=fZl7q7UgEXkC&pg=PA909 |url-status=live }}</ref> However, some halogen-free materials can also release significant amount of corrosive products.<ref>{{cite book |url=https://books.google.com/books?id=Sj4vSgMdimAC&pg=PA43 |page=43 |title=Optoelectronics for data communication |author=Ronald C. Lasky |author2=Ronald Lasky |author3=Ulf L. Österberg |author4=Daniel P. Stigliani |publisher=Academic Press |year=1995 |isbn=978-0-12-437160-6 |access-date=25 September 2016 |archive-date=16 July 2020 |archive-url=https://web.archive.org/web/20200716062706/https://books.google.com/books?id=Sj4vSgMdimAC&pg=PA43 |url-status=live }}</ref>

Smoke damage to electronic equipment can be significantly more extensive than the fire itself. [[Electrical cable|Cable]] fires are of special concern; [[low smoke zero halogen]] materials are preferable for cable insulation.<ref>{{Cite journal |last1=Szultka |first1=Seweryn |last2=Czapp |first2=Stanislaw |last3=Tomaszewski |first3=Adam |last4=Ullah |first4=Hayat |date=February 2023 |title=Evaluation of Fire Hazard in Electrical Installations Due to Unfavorable Ambient Thermal Conditions |journal=Fire |language=en |volume=6 |issue=2 |page=41 |doi=10.3390/fire6020041 |issn=2571-6255 |doi-access=free }}</ref>

When smoke comes into contact with the surface of any substance or structure, the chemicals contained in it are transferred to it. The corrosive properties of the chemicals cause the substance or structure to decompose at a rapid rate. Certain materials or structures absorb these chemicals, which is why clothing, unsealed surfaces, potable water, piping, wood, etc., are replaced in most cases of structural fires.{{citation needed|date=January 2022}}