Chapter 22 — Exercises

Work these without looking back at the chapter first; then check yourself. Items marked † have full worked solutions in the answers appendix. There are no answers in this file. The mix is recall, applied reasoning, evidence interpretation, "spot the overstatement," ethics, and a cold-case extension. Treat the Willingham and Han Tak Lee material with the sobriety it deserves.

A. Recall and definitions

  1. Define fire investigation in one sentence, and name the consensus standard (by its number) that governs modern practice.

  2. Distinguish origin from cause in an origin-and-cause determination, and explain why the cause cannot be reliably established without first correctly locating the origin.

  3. † Name the three legs of the fire triangle, and state what physically happens to a fire when any one leg is removed.

  4. Define flashover in your own words. Roughly what ceiling-gas temperature range is associated with it, and what changes in the room when it occurs?

  5. Name the three modes of heat transfer, and for each give a one-line example of how it spreads a fire.

  6. Define accelerant and ignitable-liquid residue (ILR), and state the one place — scene or laboratory — where an accelerant is actually confirmed.

  7. List the four standard cause classifications a fire investigation can reach. Which one does the chapter call "the category the old folklore could never tolerate," and why is it often the only honest answer?

  8. Define negative corpus and state, in one sentence, why it is a logical fallacy rather than a determination.

  9. What is the heat release rate, and why does the heat release rate of a modern foam sofa undermine the old claim that "an unusually hot, fast fire proves an accelerant"?

  10. Name three of the debunked fire indicators and, for each, state in a phrase what it was once thought to prove.

B. Applied reasoning

  1. † Explain mechanically why crazed glass is not evidence of arson. What actually causes crazing, and why does it appear at essentially every structure fire?

  2. An investigator finds severe, low, irregular, "pool-shaped" charring on a living-room floor and calls it a "pour pattern" proving a poured accelerant. Using flashover, give the alternative explanation and state what the honest reading of the pattern is.

  3. Walk through the four-step "self-confirming machine" by which flashover artifacts plus negative corpus can produce a false arson finding without any dishonest actor. (See §22.4.)

  4. † A fire scene is badly destroyed and no accidental cause can be identified, but there is also no confirmed ignitable liquid and no multiple origins. What is the scientifically honest cause classification, and why is "incendiary" the wrong call here?

  5. Explain why ventilation (the air supply) can make burn patterns track "where the air came from" rather than "where the fire was set," and why that matters for reading a scene.

  6. State the two kinds of affirmative evidence the chapter identifies as legitimate grounds for an incendiary finding. Why are these different in kind from the debunked indicators?

  7. An analyst gets a negative ILR result from fire debris. Does this prove no accelerant was used? Explain the asymmetry, and connect it to the exclusion-versus-proof idea from Chapter 1.

  8. A confirmed ignitable liquid (gasoline) is found in a home's attached garage where a lawnmower is stored. Does the confirmed gasoline support arson? Explain why "presence of an ignitable liquid" is not "proof of arson," and what context would change the answer.

C. Evidence interpretation

  1. † Re-read Figure 22.1 ("The 'pour pattern' that wasn't"). List what the burn pattern does show, what it does not show, and the single honest sentence an investigator could say about it.

  2. A report concludes: "The fire was incendiary because all accidental causes were eliminated and crazed glass and low burn patterns indicated an accelerant." Identify three separate methodological errors in that single sentence.

  3. Contrast two reports on the same fire. Report A: "Cause undetermined; the scene was too damaged to establish origin or cause to a reasonable degree of scientific certainty." Report B: "Cause incendiary; no accidental cause was found." Which report is more scientifically honest, and why? What is Report B actually committing?

  4. An investigator collects suspected accelerant debris into an ordinary plastic grocery bag and submits it to the lab. Name two distinct problems this creates for the analysis, and state the correct container.

  5. Explain why a competent investigator collects a comparison sample of unburned material from away from the suspected origin. What specific error does it guard against, given what modern synthetic materials emit when heated?

D. Spot the overstatement / junk-science alert

  1. † A fire investigator testifies: "In my thirty years I have seen thousands of fires, and I know an arson when I see one — the pour patterns here are unmistakable." Name the validity problem with "I know it when I see one," and the specific indicator being overstated. What would a Daubert cross-examination ask?

  2. A prosecutor's slide reads: "The crazed glass proves the fire burned unnaturally hot, which proves an accelerant, which proves arson." Identify each broken link in that chain and rewrite the slide honestly (or state that it cannot be rescued).

  3. An investigator says, "I couldn't find any accidental cause, so the only remaining explanation is that someone set it." Name the fallacy, and give the two reasons the absence of an identified accidental cause does not establish arson.

  4. A scene investigator and a laboratory chemist both testify. The chemist says "the chemical pattern is consistent with gasoline"; the investigator says "the gasoline was poured deliberately in this pattern to set the fire." Which statement is the validated analytical-chemistry claim and which is the contestable scene interpretation? Why is letting the first lend its strength to the second a classic overstatement?

  5. † A television fire investigator walks a smoking scene, points at the floor, and pronounces "arson" within a minute. Using §22.1–22.4, give two reasons this is backward from how a real determination is made.

E. Ethics and reasoning

  1. † An investigator arrives at a fatal house fire already told that the homeowner had money troubles and "seemed off." Using the Cognitive-Bias Watch in §22.3 (and previewing Chapter 31), explain how that context can bias an indicator-based examination, and what the safeguard is. Why does the ubiquity of the indicators make them perfect confirmation fodder?

  2. The Willingham investigators were probably sincere, not corrupt. Explain why that makes the case more disturbing, not less, and connect it to the Chapter 6 point about an honest examiner being the vehicle for junk science.

  3. Han Tak Lee was released after roughly a quarter-century; Cameron Todd Willingham was executed. Using the science-versus-law asymmetry (Chapter 5, §5.1), explain why the same maturing fire science produced such different endings for the two men, and what that teaches about the death penalty and unvalidated forensic methods.

  4. You are a fire investigator who genuinely cannot determine a destroyed scene's cause, but the lead detective is pressing you to "just call it arson" so the case can move. Using the affirmative-evidence standard and "undetermined," explain what you should report and why yielding would be a methodological failure, not a service.

F. Synthesis and validity spectrum

  1. † The chapter says fire investigation spans the validity spectrum. Place (a) the debunked-indicator method and (b) modern fire-dynamics-plus-confirmed-ILR origin-and-cause work on the NAS 2009 / PCAST 2016 spectrum, justify each placement, and name the feature that separates them. What other discredited method (Chapter 16) keeps the debunked indicators company at the bottom?

  2. In one paragraph, explain how this chapter advances at least two of the book's four themes (exclusion over proof; the validity spectrum; cognitive bias; the CSI effect cutting both ways). Name which themes and how.

  3. Explain how the autopsy finding of no soot in the airways (Chapter 11), the toxicology finding of a sedative (Chapter 20), and this chapter's incendiary finding fit together into a coherent staged-homicide picture — and state precisely what the fire evidence does and does not add to that picture.

G. Cold-case extension

  1. † Cold Case. Using only what this chapter's fire investigation establishes, write the entry you would add to the Mill Creek evidence log (Appendix I). State (a) the cause classification and the affirmative grounds it rests on, (b) the debunked indicators that were explicitly not relied upon and why that matters, (c) at least three things this finding does not establish, and (d) why no person's name attaches to the arson finding.

  2. Cold Case extension. The cold-case fire is found incendiary on "multiple origins + an ignitable-liquid pattern." Explain, step by step, how this finding is deliberately contrasted with the Willingham investigation so that the cold case does not commit the error it critiques. What would the wrong (Willingham-style) version of this finding have looked like?

  3. Cold Case, integrative. The chemistry bench (Chapter 21) gave a presumptive gasoline result; this chapter relies on a gasoline distribution pattern; Chapter 23 will confirm the gasoline by GC-MS. Explain the difference between "presumptive," "pattern consistent with," and "instrumentally confirmed," and why the arson finding here is honest even before the Chapter 23 confirmation lands.

  4. Cold Case. Suppose a junior investigator on the Mill Creek case wants to bolster the arson finding by adding "crazed glass and alligatoring were also present." Explain why you would decline to put those in the report even though they are "consistent with" arson, and what that decision protects.

  5. Cold Case, person vs. fire. The arson finding establishes a deliberate fire but no arsonist. List two later evidence types (from chapters previewed in the Case File) that begin to connect a person to the scene, and state plainly why the arson finding alone cannot make that leap.