I-11

Failure Mode Taxonomy

SUMMARY Reference card classifying the six failure modes of outdoor BBQ hood installations, with root causes, symptoms, and correctable vs. design-locked status.

Reviewed by Mark Zuro, outdoor ventilation product specialist with 15+ years designing and engineering outdoor-rated range hoods. Published 2025-12-10 Updated 2026-07-11

Outdoor hood failure mode taxonomy: six primary failure mechanisms (RB-007) Six cards, each with root cause, symptom, fix and a severity bar, classified per RB-007 Table 3.9. 1 Inadequate overhang (most common; design-locked): hood smaller than plume at the interception plane; symmetric smoke escape from all edges; requires hood replacement. 2 Excessive mounting height (partially correctable): all plume parameters degraded by height; diffuse, general smoke escape, plume appears wide and weak; lower the hood or raise the grill, design-locked if the mount is fixed. 3 Insufficient exhaust rate (correctable): CFM below required K_CFM times plume mass flow; edge spillage that improves when blower speed increases; upgrade blower, clean filters. 4 Wind-deflected plume escape (correctable): wind displaces plume beyond hood boundary; directional, intermittent escape correlated with gusts; add side panels, wind baffles. 5 Geometry-induced spillage (partially correctable): low effective capture area from poor internal design; uneven capture, dead zones under hood face; add baffles, lip extension. 6 Momentum-limited capture (correctable): edge velocity too low to draw in plume periphery; plume rises past hood face without being drawn in; increase CFM. Legend: red design-locked, yellow partially correctable, green correctable. Outdoor Hood Failure Mode Taxonomy Six primary failure mechanisms — RB-007 Design-Locked Partially Correctable Correctable 1 Inadequate Overhang MOST COMMON DESIGN-LOCKED Root Cause: Hood smaller than plume at interception plane Symptom: Symmetric smoke escape from all edges Fix: Design-locked — requires hood replacement Severity 2 Excessive Mounting Height PARTIALLY CORRECTABLE Root Cause: All plume parameters degraded by height Symptom: Diffuse, general smoke escape; plume appears wide and weak Fix: Partially correctable — lower hood or raise grill; design-locked if the mount is fixed Severity 3 Insufficient Exhaust Rate CORRECTABLE Root Cause: CFM below required K_CFM x plume mass flow Symptom: Edge spillage that improves when blower speed increases Fix: Correctable — upgrade blower, clean filters Severity 4 Wind-Deflected Plume Escape CORRECTABLE Root Cause: Wind displaces plume beyond hood boundary Symptom: Directional, intermittent escape correlated with gusts Fix: Correctable — add side panels, wind baffles Severity 5 Geometry-Induced Spillage PARTIALLY CORRECTABLE Root Cause: Low effective capture area (poor internal design) Symptom: Uneven capture, dead zones under hood face Fix: Partially correctable — add baffles, lip extension Severity 6 Momentum-Limited Capture CORRECTABLE Root Cause: Edge velocity too low to draw in plume periphery Symptom: Plume rises past hood face without being drawn in Fix: Correctable — increase CFM Severity OVS-RB-007 | outdoorventilationstandard.com

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Method & assumptions

This reference card catalogs the six primary failure modes observed in outdoor barbecue hood installations. Each mode has a distinct physical root cause, observable symptom pattern, and corrective classification.

Reference readings

This instrument’s taxonomy view is categorical, not numeric — the table below is the exact data set driving the interactive tree above (instruments/i10.mjs’s FAILURE_MODES array), condensed from RB-007 §3.1-3.9 and classified per its Table 3.9.

ID	Failure mode	Classification	Root mechanism
FM-1	Inadequate Overhang	Design-locked	Hood footprint at the plume interception plane is smaller than the plume’s expanded cross-section
FM-2	Excessive Mounting Height	Partially correctable	Every plume parameter degrades with height at once: wider plume, higher mass flow, lower velocity
FM-3	Insufficient Exhaust Rate	Fully correctable	Installed CFM is below the plume’s mass flow plus the required infiltration margin
FM-4	Wind-Deflected Plume Escape	Fully correctable	Ambient wind displaces the plume centerline beyond the available overhang
FM-5	Geometry-Induced Spillage	Partially correctable	Non-uniform internal velocity distribution leaves the hood perimeter under-suctioned
FM-6	Momentum-Limited Capture	Fully correctable	Exhaust-induced edge velocity is too low to overcome the plume’s outward expansion

Only FM-1 (inadequate overhang) is fully design-locked among the six catalogued failure modes; FM-2 and FM-5 are partially correctable, and FM-3, FM-4, and FM-6 are fully correctable without replacing the hood [RB-007 §3.9]. FM-1 and FM-5 both produce still-air, non-directional escape patterns, but only a wider or deeper hood fixes FM-1, while FM-5 responds to filters, baffles, or a perimeter lip without any change to the hood’s external dimensions [RB-007 §3.2, §3.6]. FM-4, the wind-deflected escape mode, is the one this program’s side-panel and CFM-sizing tools both target directly, since it is fully correctable by either intervention [RB-007 §3.5].

How to Use This Diagram

Observe the smoke escape pattern during cooking, then match it to one of the six failure modes:

Symmetric escape from all edges (still air) → FM-1: Inadequate Overhang
Diffuse, general escape; plume looks wide and weak → FM-2: Excessive Mounting Height
Edge spillage that improves when blower speed increases → FM-3: Insufficient Exhaust Rate
Directional, intermittent escape correlated with wind gusts → FM-4: Wind-Deflected Plume Escape
Uneven capture with dead zones under the hood face → FM-5: Geometry-Induced Spillage
Plume rises past the hood face without being drawn in → FM-6: Momentum-Limited Capture

Correctable vs. Design-Locked

The most important distinction: FM-1 and FM-2 are design-locked — they cannot be fixed without replacing the hood or fundamentally changing the installation. FM-3, FM-4, and FM-6 are correctable through blower upgrades, filter maintenance, or adding side panels. Getting this diagnosis right avoids wasted effort on interventions that cannot address the root cause.

Source Paper

RB-007: Failure Modes of Outdoor BBQ Hoods — Complete failure mode analysis with diagnostic decision tree

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Papers

RB-007: Failure Modes of Outdoor BBQ Hoods

HOW TO CITE

Outdoor Ventilation Standard (2025). “Failure Mode Taxonomy.” Interactive Tool, Outdoor Ventilation Standard. https://outdoorventilationstandard.com/tools/failure-mode-taxonomy/