Fire Investigation

PPE

CSI suits and hard hats used and fire scene must always be declared safe for investigation

Hazard

something with the potential to cause harm

Risk

the likelihood of harm from a hazard

Nylon bags

used for packaging fire debris or volatile liquids

Swan neck technique

Twist neck of nylon bag, tie a knot and use cable tie in double bag

Point of Origin (PO)

the point where somethings begins

Ignition source

electrical, naked flame, biological and chemical

Inner cordon

immediate scene and only people going into the crime scene

Outer cordon

evidence and escape routes and control media

Fire suppression

how the fire is extinguished

External Photography

building, openings , damage and evidence

Internal Photography

ceilings, floors, walls, doors and smoke alarms

Scene Diagrams

super detailed with measurements on CAD machines

Spalling

chipping of concerted in walls or ceilings

Thermal Expression

heat causes most materials to expand and change shape

Calcination

chemically bound water is driven out by heat

Glass

bulbs are a good indicator of the direction of fire

Fire patterns

physical changes or identifiable shapes formed by a fire effect

Plume-generated patterns

3D fire patterns where flame rises upwards until it is cooled and releases heat

Ventilation-generated patterns

well ventilated fires increase the rate material damage

Bevelling

an indicator of fire direction on wood wall studs

Char patterns

carbonaceous material created by hot fires that burn and move quickly

V-patterns

usually start at an outlet against a wall and leave a char patterns at the PO

Types of V-patterns

Narrow, wide and U-shape

Narrow V-shape

hot fire that could have had an accelerant

Wide V-shape

slow-burning fire

U-shape

indicates pool of origin such as a puddle of gasoline

Heat shadows

occurs when an object shields another which can determine the PO

Avoiding trip hazards

stepping plates and CAP

Industrial fire evidence

entry logs, keycards and fobs

Accelerant residue evidence

if wet put in breathable packaging to dry naturally and avoid degrading

Mass Loss

as exhibit burns it becomes lighter

demarcation lines

how heat moves around the object

Rainbow effect

indicates hydrocarbons could be evidence of ignitable fluids

Flame Height Equation

H_f = 0.174 x (kQ)^0.4

Temperature of Plume Equation

T_max - T_infinity = (5.38(Q/r)^2/3)/H

Combustion

an exothermic oxidation reaction where fuel reacts with oxygen to release heat energy

Combustion equation

CH₄ + 2O₂ —> CO₂ + 2HO

Fuel

materials that can burn (solid, liquid, gases)

Solid fuel

wood and electrical cable

Liquid fuel

diesel

Gaseous fuel

hydrogen

Flashpoint

minimum temperature at which liquid produces sufficient vapour to ignite

Fire point

minimum temperature to maintain combustion usually same as flashpoint

Autoignition temperature

minimum temperature at which the liquid or vapour will spontaneously ignite

Types of combustion

flammable, complete, incomplete, piloted and spontaneous

Flammable combustion

flammable gaseous pyrolysis products in the vapour phase causing flames

Sublimination

where a soil goes to gas without passing through the liquid phase

Smouldering

where a soil goes to gas without passing through the liquid phase

Complete combustion

produces only water and carbon dioxide typically a blue flame

Incomplete combustion

not enough to create carbon dioxide typically yellow or orange

Piloted combustion

an independent flame or spark in controlled setting

Spontaneous combustion

flame develops independently in uncontrolled setting

Convection

hot gases move upwards

Conduction

transfer through materials from hot to cold areas

Radiation

electromagnetic energy needs no transfer medium

Fire plume

the buoyant stream of heated air and combustion products rising above a fire

Volts (v)

difference in potential energy between two points causing a flow of electrons

Amps (I)

rate of electrons flowing

Resistance (R)

friction loss

Impedance

the total resistance to current flow in a circuit

Watts/Power (P)

energy produced

Volts equation

V= I x R

Alternating current (AC)

current switches direction positive to negative, most common form found in all devices

Direct current (DC)

current flows in only one direction found in circuits and batteries

Electricity Safety

conductors should be treated as live and always test cables

Flow of holes

absence of electrons same direction of current

Conventional current

opposite to the direction of electrons

Factors affecting resistance

cross-sectional area, length and temperature

Conductor

all metallic substances where charges move through easily and less than 4 valence electrons

Semiconductors

properties of such materials in between metallic and non-metallic

Insulators

no loosely bound electrons

UK Existing Supply System

L1 - Red

L2- Yellow

L3- Blue

N- Black

UK Harmonised (EU)

L1- Brown

L2- Black

L3- Grey

N- Blue

RCBO

Residual Current Breaker with Overcurrent

OCPDs

Overcurrent Protection Devices

OCPDs role

guard against overheating of conductor and protection from short circuits (fuses and circuit breakers)

Fuse

metal that will melt at predetermined current flow

Factor of 2

when moving upstream PDs should be at least twice the current value of the device

Fusing Factor equation

A= Minimum Fusing Factor/Current Rating

Cartridge Fuse

designed to protect device or circuit from electrical overload

Miniature Circuit Breaker (MCB)

mechanical means of opening or switching the current

Earthing Systems

maintains exposed metal parts close to zero volts to avoid human becoming apart of the circuit

Thermal Cutoffs (TCOs)

consists of metal pellets that will expand to move current in certain direction

Types of Surge Protection (SPD)

Type 1, 2, 3

Type 1 SPD

protection against direct lightning strikes

Type 2 SPD

protection against over-voltages and indirect lightning strikes (MOV)

Type 3 SPD

sensitive equipment

Metal oxide varistor (MOV)

disk of zinc oxide encased in epoxy with a connector wire on each side

Causes of Surges

sudden widespread demand, downed power-lines, bad wiring and restoration of power

Arc Fault Detection Devices (AFDD)

identify arc faults and automatically trip

Ventilation Failure

the result of an inability of an electrical device to lose heat

Localised Resistive Heating

fault causing resistive heating at specific point in a circuit

Lithium Ion Batteries

can fail releasing toxic gases like HF and CO

Insulation Failure

when conductors touch and cause a short circuit

Carbon Tracking

cellulose is an effective insulator but when heated it’s reduced to carbon

Arching

a continuous spark maintained when the gap is maintained for longer periods

Animal Welfare Act S9.2

suitable environment, suitable diet and exhibit normal behaviours for fire dogs

Fire Dog Health and Safety

not deployed into hot scenes, risk assessment, monitor dog’s welfare and keep other animals out