Criminalistics & Engineering

This chapter brings together the engineering-grade forensic specialties: cement and concrete failure analysis under the Indian Standard codes, structural steel testing, fire investigation per NFPA 921, explosive analysis, currency authentication, soil and palynology, and the diatom test for drowning. The unifying theme is the application of standardised engineering methods to forensic questions with court-defensible documentation.

7.1Cement Analysis (IS 269 / IS 4031)

Failure pattern interpretations: high insoluble residue + low strength = adulteration with inert filler. High MgO = magnesia unsoundness; free MgO hydrates slowly to brucite (117% volume expansion) over months, fracturing hardened concrete.

7.2Concrete and Steel (IS 456 / IS 1786)

IS 456 defines the concrete cube test: 150 mm × 150 mm × 150 mm cubes, cured submerged at 27 °C, tested at 7 and 28 days, loaded at ~0.6 N/mm²/s. Grade specification: M20 = 20 MPa minimum, M25 = 25 MPa, up to M60+.

IS 1786 reinforcement steel: Fe 415 = yield ≥ 415 N/mm²; Fe 500 = yield ≥ 500 N/mm²; Fe 550 = yield ≥ 550 N/mm². Below-spec rebar = significant structural risk.

IS 13920 governs ductile detailing for earthquake-resistant requirements: stirrup spacing, splice length, hook configuration, cover requirements.

7.3Fire Investigation (NFPA 921)

The V-pattern: a fire's ignition point produces a rising plume of hot gases; the plume contacts walls and chars them in a V-shaped pattern with the apex pointing back to the origin.

Floor-level apex is suspicious — most accidental fires originate higher (electrical outlets, appliances, smoking materials). The textbook arson signature combines: (1) V-pattern apex at floor level, (2) serpentine pour pattern of low-burn flooring, (3) ignitable-liquid residue (ILR) in fire-debris GC headspace per ASTM E1412 / E1618.

ASTM E1618 ignitable-liquid classes

7.4Arc Bead vs Fire-Melted Bead

7.5Explosive Residue Analysis

Organic explosives: TNT (M⁺ 227) by GC-MS; RDX, HMX, PETN by HPLC-MS/MS (non-volatile / thermolabile).

Inorganic ions (post-blast): NO₃⁻ (ANFO, dynamite), ClO₃⁻ (chlorate mixtures), ClO₄⁻ (perchlorate), SO₄²⁻ (black powder) by Ion Chromatography at ng/mL.

NH₄NO₃ phase IV (room-temperature stable form) gives characteristic XRD peaks at 2θ = 22.4°, 28.6°, 31.4° (Cu K-α).

7.6Currency Authentication (RBI)

The intaglio touch test is the single most reliable point-of-inspection feature. Industrial intaglio presses cost crores of rupees; opportunistic counterfeiters cannot access them.

7.7Counterfeit Gold (XRF)

A typical counterfeit-gold-coin XRF reading: Au 18% + Cu 60% + Zn 15% + Ni 5%. The Cu/Zn ~4:1 ratio + small Au signal = brass with thin gold plating, NOT real gold. Genuine 22-karat gold shows Au > 91%.

Confirmation: cross-section + SEM-EDX line-scan (reveals plating thickness); density measurement (Au 19.3 g/cm³ vs brass 8.5 g/cm³ — even thin plating cannot mask the difference).

7.8Soil Discrimination — Multi-Parameter Battery

1. Munsell colour (Hue / Value / Chroma) under standard daylight, wet and dry
2. Particle-size distribution — sand / silt / clay percentages
3. Major mineral content — XRD identifies bulk crystalline phases
4. Trace mineral content — LIBS / ICP-MS at ppm-ppb
5. Organic content — loss on ignition, total organic carbon
6. Soil pH and conductivity
7. Palynology — pollen species inventory after acetolysis
8. Heavy minerals — zircon, garnet, tourmaline

7.9Forensic Palynology

Pollen species + seasonal flowering windows = location attribution + seasonal estimation + post-mortem interval. Each plant species produces pollen with species-specific morphology (exine sculpting, aperture pattern, size 5–200 µm). Used in war-crime mass-grave identification, kidnapping holding-location identification, drug-origin attribution.

7.10The Diatom Test for Drowning

Diatoms in bone marrow (femur / sternum) with species match to the suspected drowning water = ante-mortem drowning. Mechanism: in life, inhaled water carries diatoms across the alveolar membrane; the still-beating heart pumps them through systemic circulation to deep tissues. In post-mortem submersion, no circulation = no transport beyond the lungs.

Caveats: tap-water drowning often has few diatoms (negative result is not exculpatory); contamination during recovery is a real concern (bone marrow chosen because external contamination unlikely to penetrate).

7.11Helmet Failure (IS 4151)

A standard-compliant helmet (IS 4151 / DOT FMVSS 218 / ECE R22) is engineered to: distribute impact across the shell, absorb energy through the EPS foam liner, retain on the head via chinstrap, and limit peak head acceleration to ≤ 250 G.

Forensic examination: shell + liner crush + chinstrap failure mode + certification verification + drop-test on a comparable helmet.