Self-heating, spontaneous ignition and thermal-criticality screening for reactive porous media — lagging fires from combustible liquid absorbed into porous thermal insulation, Frank-Kamenetskii and Semenov criticality, critical layer thickness, critical surface temperature, induction time to ignition, and Arrhenius parameter fitting from hot-storage (basket) tests per EN 15188 / ASTM E2021. USE WHEN: a task involves a flammable liquid leak or spill onto insulation or lagging, oil-soaked lagging, spontaneous combustion, self-ignition, smouldering, a fire with no obvious ignition source, insulation-material selection driven by absorbency, or fitting oxidation kinetics from oven/basket test data. Anchors on neqsim.process.safety.selfheating.
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Self-heating, spontaneous ignition and thermal-criticality screening for reactive porous media — lagging fires from combustible liquid absorbed into porous thermal insulation, Frank-Kamenetskii and Semenov criticality, critical layer thickness, critical surface temperature, induction time to ignition, and Arrhenius parameter fitting from hot-storage (basket) tests per EN 15188 / ASTM E2021. USE WHEN: a task involves a flammable liquid leak or spill onto insulation or lagging, oil-soaked lagging, spontaneous combustion, self-ignition, smouldering, a fire with no obvious ignition source, insulation-material selection driven by absorbency, or fitting oxidation kinetics from oven/basket test data. Anchors on neqsim.process.safety.selfheating.
NeqSim Self-Heating and Spontaneous Ignition Skill
Screening for low-temperature self-heating leading to spontaneous ignition —
the mechanism behind lagging fires, where a combustible liquid soaks into porous
thermal insulation and ignites with no external ignition source.
When this skill applies
Reach for this skill when you see any of these signals:
A fire or smoke event on insulated pipework, vessels or valves with no
identified ignition source.
A leak of a combustible liquid — glycol (MEG/DEG/TEG), heat-transfer oil,
lubricating oil, hydraulic fluid, amine, diesel — onto or into porous
insulation (mineral wool, glass wool, calcium silicate, perlite).
Questions phrased as "can this liquid self-ignite?", "is this insulation
safe?", "how thick can the lagging be?", "why did it catch fire hours
after the leak stopped?"
A request to interpret oven / basket / hot-storage test results, or to
extrapolate small-scale test data to plant scale.
The one thing to get right
Self-heating is a size-dependent problem, not a temperature-only problem.
Heat is generated throughout the volume (scales with $r^3$) but lost through the
surface (scales with $r^2$). So the same material at the same temperature can be
perfectly stable as a thin film and ignite as a thick layer.
This is why the lumped adiabatic screening in
neqsim.process.safety.reaction.RunawayReactionAnalyzercannot answer this
question — it assumes a well-stirred mass with no spatial conduction, so it has
no concept of a critical thickness or a critical surface temperature. Do not
substitute it. Use neqsim.process.safety.selfheating.
Equally, do not use a Gibbs/equilibrium calculation to decide whether something
self-ignites.GibbsReactor will report that any hydrocarbon is fully oxidised
to CO₂ and H₂O at 20 °C, because that is thermodynamically true and kinetically
irrelevant. Equilibrium gives you the fuel ($\Delta H$); only kinetics give you
the hazard.
Model selection
Situation
Model
Class
Liquid absorbed in insulation, internal gradients matter (Bi ≫ 1)
Frank-Kamenetskii
PorousMediaSelfHeatingAnalyzer
Drained pool, thin film, small sample; uniform temperature (Bi ≪ 1)
with $P = A,Q,\rho$ the volumetric heat-release pre-exponential factor [W/m³],
$E$ the activation energy [J/mol], $r$ the characteristic half-dimension [m],
$\lambda$ the effective conductivity of the wetted medium [W/(m·K)] and $T_a$
the boundary temperature [K]. A steady state exists only while
$\delta \le \delta_{crit}$, where $\delta_{crit}$ depends only on shape:
slab 0.878, infinite cylinder 2.00, sphere 3.32, cube 2.52, equicylinder 2.76.
Require at least three basket sizes and check getRSquared() before trusting the fit.
2. Screen the plant-scale geometry
PorousMediaSelfHeatingResultr= k
.createAnalyzer(SelfHeatingGeometry.SLAB, 50.0, "mm", 180.0, "C")
.analyze();
r.getVerdict(); // SUBCRITICAL / MARGINAL / SELF_IGNITION
r.getCriticalTemperatureK(); // hottest safe surface for this thickness
r.getCriticalDimensionM(); // thickest safe layer at this temperature
For lagging on a hot line, use the convenience configuration, which applies a
conservative bounding assumption (slab half-dimension = full insulation thickness,
boundary temperature = pipe wall temperature) and records that assumption in
getWarnings():
SelfHeatingInductionResultt=newSelfHeatingInductionSolver()
.setGeometry(SelfHeatingGeometry.SLAB)
.setCharacteristicDimension(50.0, "mm")
.setEffectiveThermalConductivity(0.09)
.setBulkProperties(150.0, 1200.0) // bulk density, specific heat
.setActivationEnergy(110.0, "kJ/mol")
.setVolumetricHeatReleasePreFactor(5.0e13)
.setBoundaryTemperature(180.0, "C")
.setMaxTime(30.0, "day")
.solve();
t.isIgnited();
t.getInductionTimeHours(); // typically hours to days — not seconds
4. Hand off the consequence
A predicted ignition is a source term, not the end of the study. Continue to
neqsim-consequence-analysis (pool/jet fire radiation) and
neqsim-relief-flare-network if the fire exposes pressurised equipment.
Input guidance and common mistakes
Input
Guidance
Common mistake
$\lambda$ effective conductivity
Use the wetted composite value; absorbed liquid displaces pore air and raises it well above the dry rating
Using the dry insulation datasheet value — non-conservative
$r$ characteristic dimension
Must match SelfHeatingGeometry.getDimensionDescription() (half-thickness for a slab, radius for cylinder/sphere)
Passing full thickness where half-thickness is expected, or vice versa
$P$ pre-factor
$P = A,Q,\rho$ where $\rho$ is reactive liquid mass per bulk volume, not the insulation density
Using insulation bulk density instead of liquid loading
$T_a$ boundary temperature
The hot process surface, not ambient air, for lagging on a hot line
Using ambient air temperature — badly non-conservative
Geometry for transient solver
Only SLAB / INFINITE_CYLINDER / SPHERE are one-dimensional
Passing CUBE to SelfHeatingInductionSolver (rejected)
Interpreting the verdict
SUBCRITICAL — a stable steady state exists. Still report the margin; the
steady self-heating excess is only a few kelvin, so there is no temperature
warning before runaway.
MARGINAL — within 30 % of criticality. Small changes in liquid loading,
thickness or surface temperature tip it over. Recommend confirmatory testing.
SELF_IGNITION — no steady state exists. Report the induction time and treat
as a credible fire scenario.
assumptions: kinetic-parameter provenance (measured vs assumed), effective
conductivity basis, and the pipe-insulation bounding assumption if used
standards_applied: EN 15188, ASTM E2021 for the test method
Carry every entry of getWarnings() into the assumptions/gaps register
Mitigation hierarchy (for recommendations)
Eliminate absorbency — closed-cell or non-absorbing insulation, so there is
no porous matrix to hold the liquid and trap the heat. This removes the
mechanism rather than managing it, and is normally the correct recommendation.
Prevent wetting — eliminate the leak; fit liquid-tight cladding and
drainage that sheds leakage clear of the lagging.
Reduce thickness below the critical dimension, or lower the surface
temperature below the critical temperature.
Detect and inspect — remove and replace contaminated insulation promptly;
note that detection is weak as a sole barrier because the pre-runaway
temperature signature is only a few kelvin.
Related skills
neqsim-process-safety — HAZOP guideword Other than → self-ignition, LOPA, risk matrix
neqsim-consequence-analysis — fire radiation once ignition is predicted
neqsim-reaction-engineering — KineticReaction if a full reactor model of the oxidation is needed
neqsim-hazid-fmea-eta-fta — placing the scenario in an event tree
neqsim-standards-lookup — EN 15188, ASTM E2021, insulation standards
