Thermal stratification characterisation of large tunnel fires under forced ventilation

Thermal stratification characterisation of large tunnel fires under forced ventilation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermal stratification characterisation of large tunnel fires under forced ventilation Nigel Charles Dhlamini, Reshendren Naidoo, Wei Hua Ho This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9048432/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Large tunnel fires exhibit thermal stratification dynamics that are distinct from small fires, yet most existing correlations for smoke stratification are derived from small-scale or reduced-scale experiments. This computational study investigates thermal stratification in tunnels using two high-intensity fires (30 MW and 80 MW) under varying ventilation velocities. Unlike previous research that assumes ambient floor temperatures, the results show that large fires generate floor temperatures significantly above ambient due to radiative heat transfer from the extended ceiling flame. The critical temperature ratio for stable stratification was found to be $\Delta T_{cf}/\Delta T_{avg} = 1.9$, compared to the traditional value of 1.7, with a corresponding critical Froude number of 0.858. A new empirical correlation relating the temperature ratio to the Froude number is proposed and compared against existing correlations from the literature. The discrepancy in critical Froude numbers reported across previous studies is discussed, and the limitations of the Froude number as a sole descriptor of stratification stability in large fires are highlighted. stratification stability thermal buoyancy Froude number tunnel fire smoke behaviour large fires Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 28 Apr, 2026 Reviewers agreed at journal 27 Apr, 2026 Reviews received at journal 19 Apr, 2026 Reviewers agreed at journal 13 Apr, 2026 Reviewers agreed at journal 23 Mar, 2026 Reviewers invited by journal 19 Mar, 2026 Editor assigned by journal 13 Mar, 2026 Submission checks completed at journal 10 Mar, 2026 First submitted to journal 06 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9048432","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":608879267,"identity":"ba812bc5-a64f-44b2-85d3-8fb2952c4110","order_by":0,"name":"Nigel Charles Dhlamini","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6UlEQVRIie3RMQrCMBSA4VcqdYl1TajEK0Q6CR4mQejmDRwqQruIJ/ASIjgrhbroHtDBXQfdinQwts5pRsH8Q0IgH0kIgM32i0k3Bg4Yee3YmDgfMqI+2n2WzJAARCHF3JD451lyvb4ykZBbFKBpCd105z4KDSGXfcrEUpFgsg1QzgAfOQwWGsKkSLBYfEknVheTABwZEXKqSV+RfdlEeBGFHu7UhElw5rpTSHVKPKIemmyGqzxEg6OYuz0N8eU4J0WJUT89reV9Sik9ZNnzriFVTlJNLawGdaXqp5qqX+s+DLbabDbbH/YGiNBPx+63N7AAAAAASUVORK5CYII=","orcid":"","institution":"University of the Witwatersrand","correspondingAuthor":true,"prefix":"","firstName":"Nigel","middleName":"Charles","lastName":"Dhlamini","suffix":""},{"id":608879268,"identity":"9ed5233d-e0e6-4881-8528-a65819b99947","order_by":1,"name":"Reshendren Naidoo","email":"","orcid":"","institution":"University of the Witwatersrand","correspondingAuthor":false,"prefix":"","firstName":"Reshendren","middleName":"","lastName":"Naidoo","suffix":""},{"id":608879269,"identity":"dd9529e9-ba39-4941-993a-5760e0b834f8","order_by":2,"name":"Wei Hua Ho","email":"","orcid":"","institution":"University of Cape Town","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"Hua","lastName":"Ho","suffix":""}],"badges":[],"createdAt":"2026-03-06 09:08:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9048432/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9048432/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105727769,"identity":"b3e89d30-b06f-4690-9884-2b1ff21fb18e","added_by":"auto","created_at":"2026-03-30 11:03:24","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":574218,"visible":true,"origin":"","legend":"","description":"","filename":"DhlaminiStratification.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9048432/v1_covered_9ee80590-f35f-4e74-b9fb-8623e875d8d8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermal stratification characterisation of large tunnel fires under forced ventilation","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"fire-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"fire","sideBox":"Learn more about [Fire Technology](http://link.springer.com/journal/10694)","snPcode":"10694","submissionUrl":"https://submission.springernature.com/new-submission/10694/3","title":"Fire Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"stratification stability, thermal buoyancy, Froude number, tunnel fire, smoke behaviour, large fires","lastPublishedDoi":"10.21203/rs.3.rs-9048432/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9048432/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Large tunnel fires exhibit thermal stratification dynamics that are distinct from small fires, yet most existing correlations for smoke stratification are derived from small-scale or reduced-scale experiments. 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