Chapter 09

© 2009 Delmar, Cengage Learning

Sources of Ignition

Chapter 9


Objectives

• Describe various heat sources capable of being a source of ignition

• Describe how the forces of nature can provide sufficient energy to be potential heat sources

• Describe how smoking materials can be a potential heat source

• Describe how chimneys can contribute to a fire • Describe spontaneous ignition • Describe the role of appliances in ignition


Case Study• Faced with the cost of a new chimney, a

homeowner decided to purchase a woodstove and stove pipe to connect the furnace to the existing chimney with a chimney thimble

• The siding, wall sheathing, sheetrock, and wood paneling—all of which are quite combustible—served to hold the thimble in position

• Huge amounts of smoke started pouring into the room once the fire was kindled


Introduction

• Sources of ignition are all around us • Through history, primary igniters used by people

have changed– Open fire– Matches and lighters

• First thing that must be identified is the area of origin

• Then search for the first material ignited


Competent Ignition Sources

• A heat source must be able to deliver enough heat to cause ignition– There must be sufficient heat – The heat must also be in contact with the first material

ignited for a sufficient duration


Lightning

• Lightning is a static discharge between two differing potentials

• Lightning contains a lot of energy, more than enough to start a fire if conditions are right

• There may or may not be obvious indications of a lightning strike on the structure– Clues to look for include vaporized copper– Witness accounts


Seismic Events and Escaping Gas

• A seismic event is not a source of ignition – However, the event itself changes the dynamics of

the environment • Example: Great 1906 fire of San Francisco

– Primarily resulted from open flames, building destructions, and a multitude of fuel

• Smaller seismic events can create fractures in rock that release methane gas


Radiant Heat

• Sunlight is the ultimate radiant heat, but by itself is not intense enough to ignite common combustibles– When focused, can produce enough energy to be a

competent ignition source • Can be done with glass such as a magnifying glass, a

glass sphere, or pieces of broken glass capable of refracting light and focusing a beam

• No indication that this is a frequent event


Smoking Materials

• Cigarettes, cigars, and pipes are common smoking materials– Cigars are less frequently considered a fire hazard

• Go out if left unattended

– Pipes also tend to go out – The common cigarette is the culprit that has been

blamed for many fires• A cigarette will continue to burn when left unattended or

when carelessly discarded


Matches

Figure 9-4 The windand waterproof match has a higher chemical contentas can be seen in comparison of the safety match in the bottom of the photo. The strike anywherematch may have two colors which would indicatethe two chemical components necessary for the reaction.


Matches as Evidence

• Because of its size, the residue match is not always easy to locate

• When found, first consideration is whether suppression activities moved it to that location or whether it was there before the fire actually started

• Laboratory can compare the cardboard match against the matchbook– Looking at width, color, thickness, and composition


Lighters

• Two liquid fuel lighters are on the market today – Older style is usually metal and has a fuel cavity that

can continually be refilled with lighter fluid• Lighter fluid is usually naphtha and sometimes benzene

– Predominant lighter in use today is the disposable butane lighter

• Piezoelectric ignition: certain crystals that generate voltage when subjected to pressure (or impact)

• There may be latent prints on the surface of the lighter


Hobby Micro Torch

Figure 9-5 Thismicro torch, whichuses butane, isonly 4 inches longand can easily becarried in a pocket.


Other Hobby Ignition Sources

Figure 9-6 Modelrocket motors andtheir igniters canbe found in hobbystores.


Friction Heating

• Friction heat is created when two items rub together sufficiently to produce heat

• This can translate kinetic energy into thermal energy


Rotors

• Part that rotates in an electrical motor• Stationary part of a motor is called a stator • By their very nature these electric motors and

alternators get warm when working properly


Brakes

• Vehicles have rotors associated with the braking system

• Source of heat in most braking system failures is usually involving the brakes themselves


Muffler Systems

• Mufflers of motor vehicles or other metal parts hanging down sufficiently to touch the ground can become a source of sparks

• When dealing with sparks from a motor vehicle the investigator will have to depend on eye witness accounts


Sparks from Catalytic Converters

• A catalytic converter is a device designed to reduce the toxicity of emissions from engines

• Reaches high temperatures • Most manufacturers provide adequate shielding

around the catalytic converter to dissipate as much heat as possible

• Certain conditions can cause a catalytic converter to be hazardous– Impact injuries


Chimneys and Fireplaces

• Only when construction is improper or chimneys are not used properly can they be involved in an unwanted fire

• Properly used and maintained, today’s chimneys provide few problems and can be an asset to any home or business


Metal Chimneys for Fireplaces

Figure 9-7 Burnpattern of a firethat started at thefirebox of a zero-clearance Stove with metal chimney.Notice that thewooden chimneychase, with theexception of thebase, has beenconsumed.


Brick Chimneys for Fireplaces or Woodstoves

Figure 9-11 The liner extending above the brick indicates thechimney is lined.


Wind-Blown Sparks

• Wind can cause a burning object to become more incandescent – Raises its temperature– If the burning particles are small enough, the wind can

pick them up and deposit them elsewhere


Chimneys and Wind

• Wind can have an amazing affect on both chimneys and sparks– Can cause a down draft, possibly blowing sparks into

the room – Bernoulli effect: wind blowing across the top of the

opening of the chimney creates a strong updraft• Negative pressure pulls up sparks or large embers into

the chimney and out onto the roof or surrounding area


Burning Leaves

• When a leaf-burning event gets out of control, it is usually because of human error

• Pile of debris and ash may serve as an indication of a potential heat source

• Wind at the time of the fire may indicate a direction


Trash Burning

• Piling up trash and burning it is hazardous because of the toxic gases released

• When trash is placed in an open burn barrel, the sparks can rise in the hot air currents


Chemical Reactions

• Several chemicals when combined with others react, releasing heat at sufficient levels to ignite nearby combustibles


Spontaneous Combustion

• Must be an exothermic reaction taking place at normal temperature and in presence of oxygen

• Reaction must accelerate rapidly as the temperature increases

• Arrangement of the material must be such that it does not allow, or drastically limits, the dissipation of the building heat

• Material undergoing this process must be capable of smoldering


Drying Oils

• Include linseed oil, tung nut, or fish oil • All susceptible to spontaneous heating • Reaction is dependent on the percentage of the

oil in contact with oxygen along with the ability to dissipate heat


Hay and Straw

• Self-heating of hay or straw is one of the more well known spontaneous ignition events– Evaporation of moisture releases heat– Fermentation by microorganisms causes heat release – Because of the nature of this event and the ready

supply of fuel, all too often the fire results in major destruction


Plywood and Pressboard

• If sheets are stacked in such a way as to prevent the dissipation of heat, self-heating will take place


Appliances

• Appliances come in various sizes, small and large– The larger appliances can be categorized as being

electric or gas

• Investigators must first determine whether the appliance was involved in the ignition sequence


Small Appliances

• Misuse and abuse of small appliances cause failures that result in fire

• Toaster ovens easily ignited when misused• Portable heaters have been a serious problem,

especially in the workplace• Small appliances can also be used to set fire

intentionally– Using timers


Larger Appliances

Figure 9-14 Smallheater in the closetarea became ahazard when theoccupant stuffeddirty clothes inand around thewater heater,forcing combustiblematerials up againstthe unit.


Light Bulbs

• The proper wattage light bulb in a light fixture does not cause a problem

• When bulbs of higher wattage than recommended are used, heat can build up


Animals and Insects

• Animals and insects are not frequently involved in an ignition sequence


Summary

• We are surrounded by potential heat sources every day

• This chapter covers only a few potential heat sources

• Identification of the heat source must be done scientific and accurately

• Must be able to research and uncover information about all aspects of the potential heat source

Chapter 09

Business

Transcript of Chapter 09