chemical hazards and reactions

8/2/2019 Chemical Hazards and Reactions

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Chemical Hazards andReactions

Chemical hazards andreactions


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5/5/2012 2003 Seton Identification Products 2

Introduction

Chemical hazards andreactions: Chemicals are the most

common and significanthealth hazards

Chemicals can behazardous fornumerous reasons andcan combine with otherchemicals to make new

hazards All hazards must be

taken into accountwhen using and storingchemicals.


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Objectives

At the end of this module,you will be able to: Recognize chemical

hazards commonly

encountered in the field Provide examples of

physical and chemicalcharacteristics ofcontaminants

Explain warningproperties of various

chemical hazards Describe how to evaluate

and control thesehazards.


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The degree of hazardassociated with aparticular chemical will

depend on: Its physical properties

Its toxicity

The way it is used

The environment inwhich it is encountered.


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Physical Classification

Solids Aerosols

Liquids Vapors

Chemicals may be found insolid, liquid, aerosol, or gasand vapor form.

The degree of danger variesaccording to the form of thechemical and the factorspreviously discussed.


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Solids

Not all forms of a chemicalpose a health hazard.

For example, a lead pipe isnot a significant health hazard.

However, the lead canbecome a human healthhazard if the pipe is sanded orwelded, producing lead dust orfumes.

The dust or fumes canbecome airborne and beinhaled, or it can leach intowater and be ingested.


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Solids

A chemical may be hazardouseven in solid form.

For example, individuals whoare sensitized to nickel maydevelop dermatitis from skincontact with the metal.

Fuming solids emit toxicvapors that may be inhaled.

Some materials, such aspesticides, can evaporatedirectly from solid form.

Some solids are not a hazardalone but become hazardouswhen they come into contactwith other chemicals (e.g.,acid in contact with iron canrelease hydrogen gas).


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Aerosols

Aerosol is a term used todescribe fine particles(solid or liquid) suspendedin air.

Examples of aerosolsinclude dust, fumes, mist,fog, smoke, and smog.

Knowing how variousaerosols are generated willhelp you anticipate where

aerosol hazards may existin the field Aerosols may be a hazard

to the eyes, skin, and therespiratory system.


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Liquids

Many liquids are hazardous incontact with the skin. Theyeither damage the skin or theyare easily absorbed throughthe skin.

It is important to rememberthat chemicals that candamage or be absorbedthrough the skin will have thiseffect on all skin, not just thehands.

The degree of hazard

associated with a liquiddepends on its characteristicsand how it is handled.


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Liquids

For example, inhalation is theprimary route for a chemical toenter the body. Its vaporpressure is important indetermining the liquid degree

of hazard. Liquids with a low vapor

pressure may create a lowairborne concentration.

Liquids with a high vaporpressure may produce highairborne concentrations.

The hazard level of anairborne concentrationdepends in part on thechemical's toxicity.


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Liquids

Some chemicals help othercontaminants to penetrate theskin.

Dimethyl sulfoxide(DMSO) isextremely well absorbed and is

used in medicine to transportdrugs through the skin. Liquids present a splash

hazard. Appropriate protective

equipment (e.g., goggles,faceshield) and clothing (e.g.,gloves, coveralls) must be worn

to prevent contact with eyesand skin. Liquids present a splash

hazard.


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Liquids

Appropriate protectiveequipment (e.g., goggles,faceshield) and clothing (e.g.,gloves, coveralls) must be wornto prevent contact with eyesand skin.

Some liquids combine easilywith other chemicals to producehazardous substances.

Household bleach, combinedwith ammonia-based cleaningsolutions, produces asubstance that is much more

hazardous than either of thetwo original components


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Vapors

A gas is a state of matter inwhich the molecules areunrestricted by cohesiveforces.

Vapors are the evaporationproducts of chemicals thatare normally liquid at roomtemperature.

Routes of entry associated

with gases and vapors areinhalation, and eye or skinexposure.


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Test Your Knowledge

The degree of a chemical hazard dependsupon certain properties. Click on the

physical classifications which are potentialskin hazards.

Vapors

Solids

Liquids

Gases


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Physical and ChemicalCharacteristics

Knowing the physical andchemical characteristics of thechemicals you anticipate findingduring a field activity can help yourecognize potential hazards andappropriately protect yourself.

You can find the details on thephysical and chemicalcharacteristics by referring to thechemical's Material Safety DataSheet (MSDS). MSDSs must bereadily available in work areaswhere the hazardous materialsare being used.

More information about MaterialSafety Data Sheets is found in theHazard Communication module.

Autoignition Solubility

Specific Gravity Vapor Density

Vapor Pressure Boiling Point

Melting Point Flashpoint

Explosive Limits


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Autoignition Temperature

The temperature atwhich a product canundergo spontaneous

ignition is called theautoignitiontemperature.

This temperature isvery high - commonly

in the hundreds ofdegrees.


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Specific Gravity/Density

Specific gravity (SpG) is the ratioof the density of a substance (at agiven temperature) to the densityof water at the temperature of itsmaximum density.

Numerically, SpG is equal to thedensity in g/cc, but is expressedas a pure number without units.

If the SpG of a substance isgreater than 1 (the SpG of water),it will sink in water (e.g.,methylene chloride).

The substance will float on water if

its SpG is less than 1 (e.g.,oil/petroleum products). This is important when

considering containment, cleanup,disposal and treatmentalternatives.


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Specific Gravity/Density

Specific gravity (SpG) is theratio of the density of asubstance (at a giventemperature) to the density ofwater at the temperature of its

maximum density. Numerically, SpG is equal to

the density in g/cc, but isexpressed as a pure numberwithout units.

If the SpG of a substance isgreater than 1 (the SpG of

water), it will sink in water(e.g., methylene chloride).

The substance will float onwater if its SpG is less than 1(e.g., oil/petroleum products).


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Vapor Pressure

The pressure exerted by avapor against the sides of aclosed container is calledvapor pressure.

Vapor pressure is temperaturedependent.

As temperature increases, sodoes the vapor pressure.

Thus, more liquid evaporates,vaporizes or volatilizes.


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Vapor Pressure

The lower the boiling point ofthe liquid, the greater thevapor pressure it will exert at agiven temperature.

Values for vapor pressure aremost often given asmillimeters of mercury (mmHg) at a specific temperature.

Usually the higher the vapor

pressure, the more volatile thesubstance.


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Melting Point

Melting point is the temperature atwhich a solid, when heated,changes to a liquid.

This temperature is also the

freezing point, since a liquid canchange phase to a solid.

The proper terminology dependson the direction of the phasechange.

If a substance has beentransported at a temperature thatmaintains a solid phase, then achange in temperature may causethe solid to melt.


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Melting Point

A particular substance may exhibittotally different propertiesdepending on phase.

One phase could be inert while

the other is highly reactive.

Thus, it is imperative to recognizethe possibility of a substancechanging phase due to changes inthe ambient temperature.


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Solubility

Solubility is important whendetermining health effects,reactivity, dispersion, andmethods of cleanup and

treatment.

Solubility is generallyexpressed in parts permillion (ppm) or as a

percentage (0-100%).


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Vapor Density

The density of a gas or vapor canbe compared to the density of theambient atmosphere.

Vapor or gas that is greater in

density than the ambient air tendsto settle to the lowest point.

Vapor density close to the densityof air or lower tends to disperse inthe atmosphere.

In settling, dense vapor (v.d. >1)creates many hazards. If thevapor displaces enough air toreduce the atmosphericconcentration of oxygen below16%, asphyxia may result.

Material Vapor Density

Ammonia 0.59

Ethelyene 0.972

AIR 1.0

Butane 2.04

Freon-12 4.17


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Vapor Density

If the vapor is toxic, inhalationproblems predominate even if theatmosphere is not oxygendeficient.

If a substance is explosive andvery dense, the fire/explosivehazard may be in the form ofvapor trails which can spread farfrom the liquid.

Flashback can occur if an ignitionsource is present.

Material Vapor Density

Ammonia 0.59

Ethelyene 0.972

AIR 1.0

Butane 2.04

Freon-12 4.17


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Boiling Point

Boiling point is thetemperature at which liquidchanges to a vapor, or thetemperature when thepressure of the liquid equals

atmospheric pressure. The opposite change in phase

is the condensation point. A major consideration with

toxic substances is how theyenter the body.

With high-boiling-point liquids,the most common entry is bybody contact (skin absorption).

Low-boiling-point liquids aremost commonly inhaled.


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Flashpoint

Flashpoint is the lowesttemperature at which a liquidgives off enough vapor to forman ignitable mixture with airand produce a flame when an

ignition source is present. If the ambient temperature is

right, then the materials maygive off enough vapor at itssurface to allow ignition by anopen flame or spark.

When a vapor does ignite,

combustion can continue aslong as the temperatureremains at or above theflashpoint.


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Explosive Limits

The range of concentrations ofgases in air which will support theexplosive process is bounded bymeasurable limits called UpperExplosive Limits (UEL) or UpperFlammable Limit (UFL) and Lower

Explosive Limits (LEL) or LowerFlammable Limit (LFL).

The flammable range is theoptimal chemical fuelconcentration in air for the ignitionand the sustenance ofcombustion.

The lowest concentration of fuel inthis range is the LEL/LFL.


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Explosive Limits

The highest ratio that is flammableis the UEL/UFL.

Concentrations less than theLEL/LFL are not flammable

because there is too little fuel, thatis, the mixture is too lean toburn.

Concentrations greater than theUEL/UFL are not flammablebecause there is too much fueldisplacing the oxygen (resulting in

too little oxygen). The mixture istoo rich to burn.


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Test Your Knowledge

Vapor pressure is the pressure exerted by a vaporagainst the sides of a closed container.

If vapor pressure is temperature dependent, what

does a container of liquid with the sides pushed outmean?

The container was exposed to cold temperatures.

The container was exposed to heat.

The container is leaking. The container is old.


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Warning Properties

Warning properties, suchas those shown below, areexamples of characteristicsthat could alert you to the

presence of a chemical inthe air.

Odor threshold

Color of product

Other senses


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Odor Threshold

The odor threshold is the airborneconcentration at which ahazardous chemical can bedetected by smell.

This concentration of gas or vaporis expressed as parts per millionparts (ppm) of air.

This odor threshold is consideredto be one of the warningproperties of gases and vaporsbut must always be used withcaution because of variationsbetween individuals and theirsenses of smell.

Allergies, head colds, andolfactory fatigue also can reduceone's ability to smell.


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Odor Threshold

Ammonia is a good example of a chemical with a useful odor threshold. Someindividuals can detect ammonia at 5 ppm which is below the average of 17 ppm.

It is also 10 times lower than its OSHA Permissible Exposure Limit (PEL). Since the odorthreshold can warn you well before the Threshold Limit Value (TLV) and PEL arereached, ammonia is said to have adequate warning properties.

Another reference indicates that Methyl Formate has an odor threshold of 2,000 ppm,

which is 20 times higher than its PEL of 100 ppm. Thus, it is dangerous to rely on methylformate's odor as a warning property.

Material Odor Threshold (ppm) PEL (ppm)

Acetone 62 1000

Ammonia 5 50

Hydrazine 3.7 1

1,1,2 - Tricholoroethelyene 82 100Methyl Formate 2000 100

Hydrogen Sulfide (H2S) 0.3 10 (ceiling limit)


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Odor Threshold

Some chemicals can be detected easily by smell initially but can then causeolfactory fatigue or the loss of ability to smell the substance.

H2S causes olfactory fatigue and causes paralysis of the olfactory nerves. Relying on sense of smell can provide a false and potentially fatal sense of

security with an extremely toxic gas.

Never use your nose as a quantifier of chemical concentration or as a deviceto determine whether or not the air is safe.

Material Odor Threshold (ppm) PEL (ppm)

Acetone 62 1000

Ammonia 5 50

Hydrazine 3.7 1

1,1,2 - Tricholoroethelyene 82 100Methyl Formate 2000 100

Hydrogen Sulfide (H2S) 0.3 10 (ceiling limit)


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Color of Product

Color can present a visualindication of the presenceof a potentially hazardouschemical.

Two examples are fumingnitric acid, which creates ared cloud, and chlorine gas,which has a greenish color.

Both of these materials arehighly toxic.


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Other Senses

Mild irritation of the eyes,nose, or throat can be auseful warning property if itoccurs at a concentration

that does not produce otherharmful or toxic effects.

Some chemicals willproduce a taste before, or

instead of, odor or irritation.


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Test Your Knowledge

Odor threshold is the concentration at whicha hazardous chemical can be detected bysmell.

However, ________________ impair(s) thebody's ability to smell.

Allergies

A head cold

Olfactory fatigue

All of the above


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Chemical Use

The way a chemical is usedwill have a significantinfluence on the degree ofhazard associated with its

use.

Careful review of theprocess and a walk-throughinspection of the work areawill provide usefulinformation to helpanticipate potentialexposure points.


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Other EnvironmentalFactors

Four environmentalfactors that can havean impact on potential

hazards are:

Wind

Humidity

Precipitation Temperature


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Test your knowledge:

Effect Environmental FactorPrecipitation Temperature Humidity Wind

Increases or

deceases thegeneration ofstatic electricity

Can causeincompatiblereactions

Changes the airquality byspreading aircontaminants

Can increaseevaporationrates


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Test your knowledge:

Effect Environmental FactorPrecipitation Temperature Humidity Wind

Increases ordeceases thegeneration ofstatic electricity

Can causeincompatiblereactions

Changes the airquality byspreading aircontaminants

Can increaseevaporationrates


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Fire and Explosion Hazards

During field work you maybe exposed to on-sitematerials that areflammable, burn rapidly orare explosive.

Such materials may also bepresent as a part of yourown work: either in theemissions or dischargesbeing monitored, in thechemicals used for field

test procedures, or in thesolvents used for cleaningsampling apparatus.


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Combustion and Fire

Combustion is any chemicalprocess accompanied by theemission of light and heat.

When a flame is produced, as wellas light and heat, the combustionprocess is known as fire.

Some fires can be deceiving. Analcohol fire can go undetectedduring daylight because the flameis invisible.

A fire requires four components: Combustible material (fuel

source)

Oxidizing substance (usually theoxygen in the atmosphere) Ignition energy (heat or spark) Chain reaction (chemical).

C


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Combustible Materials andContributing Factors

The following factors contribute to the occurrence of a fire orexplosion of combustible materials:

Vapor pressure

Area of material from which evaporation can occur Amount of material needed to produce flammable concentrations Temperature of the material Ambient temperature Specific gravity Vapor density

Oxygen concentration Source of energy for ignition Ventilation.


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Flammable Materials

Four types of flammable materials areshown below:

Flammable Liquids

Flammable Gases

Flammable Solids Pyrophoric Liquids


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Flammable Liquids

The U.S. Department ofTransportation (DOT), theOccupational Safety andHealth Administration (OSHA),and the National Fire

Protection Association (NFPA)have established definitionsfor flammability based on theflashpoint of a material.

DOT defines flammableliquids as having flashpointsbelow 140F.

OSHA and NFPA defineflammable liquids as havingflashpoints below 100F.

Examples ofFlammable

Liquids

Gasoline

Acetone

Lacquer thinner

Methyl ethylketone

Isopropyl alcohol


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Flammable Gases

A compressed gas isconsidered flammable when:

A mixture of 13% or less withair forms a flammable mixture

- OR -

The flammable range with airis wider than 12% regardlessof the lower flammable limit.


Gases

Hydrogen

Methane

Acetylane


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Flammable Solids

Many metals and non-metals have fire-relatedhazardous properties andnearly all will burn under

certain conditions.

Flammable solids can bereadily ignited throughfriction and retained heatfrom manufacturing orprocessing.


Solids

MetallicMagnesium DustAluminum Dust

Non-MetallicCamphor

Red Phosphorous


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Pyrophoric Liquids

A pyrophoric liquid isany liquid that ignitesspontaneously in dry

or moist air below130F.

Examples ofPyrophoric

Liquids

Organmetalliccompounds

Dimethyl zinc

Tributyl Aluminum


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Explosives and Ordnance

Explosives: Explosives are

substances thatundergo a very rapid

chemicaltransformationproducing largeamounts of gases andheat.

Ordnance:

Ordnance refers toexplosive militaryweapons andammunition.


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Explosives

Explosives produce gases like nitrogen,oxygen, carbon monoxide, carbon dioxide,and steam.

Due to the heat produced, these gasesrapidly expand at velocities exceeding thespeed of sound creating both a shock wave

and noise. Low or Deflagrating

High or Detonating

L D fl ti


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Low or DeflagratingExplosive Hazards

Rate of deflagration isup to 1000 feet persecond -- slower than

high explosives. The combustion

process forms theshock wave.

Examples: smokeless

powder, photographicflash powders, solidrocket fuel.

Hi h D t ti


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High or DetonatingExplosive Hazards

The rate of detonation can be ashigh as four miles per second.

A shock wave may be followed bycombustion because the gasesproduced are flammable.

Primary high explosives may bedetonated by shock, heat, orfriction producing a detonativewave in an extremely short periodof time. Examples are: lead azide,

mercury fulminate, and leadstyphnate.

Hi h D t ti


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High or DetonatingExplosive Hazards

Secondary high explosivesgenerally need a booster tocause detonation.

They are relatively insensitive

to shock, heat, or friction. Examples are: Tetryl,

cyclonite, dynamite, andTNT.


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Ordnance

Whenever the presence of unexplodedordnance (UXO) such as grenades,shells, mines, and other explosivedevices is a possibility, personnel andsupport shall be provided withequipment necessary to locate, identify,recover/remove/dispose, and

consolidate all ordnance or energeticitems from work areas. These efforts shall be conducted in a

safe and environmentally soundmanner by qualified and trainedpersonnel (e.g., Army, bomb squad).

Prior to starting work, it isrecommended that all field personnelattend general orientation sessions that

include lectures and visual training aidscovering the various types of ordnance.

Preventing Fires and


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Preventing Fires andExplosions

Fires and explosionscan be prevented byevaluating possible

hazards and takingmeasures to eliminateand control hazardsources.


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Hazard Evaluation

Identify which materials may bepresent and get information fromreliable and knowledgeablesources on their hazards.

Use instruments (combustible gasindicators) to see if there is a

flammable concentration of vaporsor gases in the working area.(Note: Certain field equipment andinstrumentation that is battery orline-powered is not safe for use inflammable atmospheres becausethe electrical elements are notprotected from exposure to

flammable vapors or gases, orcombustible dusts.) Take precautions as if the hazards

do exist even if you are not sure.


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Hazard Control

To prevent the combustionprocess, measures must be takento reduce or eliminate one or moreof the four components (fuel,oxygen, heat, chemical chainreaction) needed for combustion.

Safe work practices and controlsshould especially be used whensampling, handling or working withflammable materials.

The four combustion components

are identified by the words fuel,oxygen, heat, and "chainreaction". Click on the words toreview these control measures.

FUEL

OXYGEN

HEAT

CHAIN REACTION


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Fuel

Remove the fuel source if possible.

Ventilate the area to reduce or eliminate

high vapor concentrations. Cover the fuel with a non-flammable

substance (e.g., fire-fighting foam) toprevent mixture with air.

Control vapor trails to prevent flashback.

Control vapor emissions.


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Oxygen

Oxygen is the most difficult portion of a fireto control because it is always present(20.9%) in the air.

Oxygen rich atmospheres (> 23.5%) presentadditional hazards (hotter burn, increasedlikelihood of ignition) that can be lowered by

utilizing dilution ventilation (blowing).


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Heat

Control all ignition sources by using explosion-proof lightingequipment and spark-resistant tools.

Extinguish and prohibit open flames and spark-producingequipment in the work area.

Sources of ignition include matches, cigarette lighters,electrical switches and equipment, welding sparks, enginesand catalytic converters on motor vehicles.

Control temperature when possible. Bond and ground all equipment.

Metal to metal contact is essential and can be accomplished

by using grounding rods or metal water pipes (cold). Scrape painted surfaces to ensure proper connections.


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Chemical Chain Reaction

Excess heat from the exothermic reaction of combustionradiates back to fuel to produce vapors and cause self-ignition.

Three factors control the occurrence of self-heating and self-ignition resulting from uninhibited chain reactions:

Rate of heat generation.

Reduce heat by eliminating the ignition source and applyingfire suppressants (water, chemical agents)

Effects of ventilation. Increase ventilation to carry awayexcess heat or decrease ventilation to eliminate oxygen

Insulating effects of immediate surroundings. Avoid piling combustible materials in confined spaces;

separate burning materials and remove insulating materials.


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Static Electricity

Static electricity is generated bycontact and separation ofmaterials, such as particulatesmoving through a stack, gasflowing from a nozzle at highvelocity, or pouring or spraying of

non-conducting liquids or solids.

Static electricity is also generatedwhen: Materials flow through pipes,

hoses, ducts A belt runs over a pulley A person walks across a floor.

Static electricity accumulates tohigher voltages in atmosphereswith low humidity and during dryweather.


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Static Electricity Prevention

It is important to recognizeactivities that generate staticelectricity since it can providesufficient energy to igniteflammable concentrations ofgases and vapors.

Practical measures to preventaccumulation or allow discharge ofstatic electricity in field activitiesinclude the following:

Grounding all probes used forstack sampling

Providing a bonding connection

between metal containers whenflammable gases or liquids aretransferred or poured

Wearing footwear with adequateconductivity for the conditions.


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Test Your Knowledge

What is a difference between detonating anddeflagrating explosives?

Deflagrating is generally combustion followed by a shockwave

Detonating explosives have a detonation rate of 1000 feetper second, and deflagrating have a rate of 4 feet persecond

Detonation can only be caused by shock, heat, or friction

and deflagration can only occur if there is a booster None of the above


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Corrosion/pH

Corrosion is a process ofmaterial degradation or theability of a material to increasethe hydrogen ion or hydroniumion concentration of anothermaterial.

The pH of a solution is thehydrogen ion concentration.Measurements of pH arevaluable because they can bequickly done on-site (e.g., pH

paper, pH meter), providingimmediate information on thecorrosive hazard.


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Corrosives

Acids Corrosives which form the greatest

number of hydrogen ions are thestrongest acids.

Bases

Corrosives which form the greatestnumber of hydroxide ions are thestrongest bases.

Bases are also called alkaline materialsor by the generic term caustic.

Halogens Corrosives which are most often found

in the gaseous state. They are considered corrosive because

contact can lead to burns, irritations,and destruction of organic tissues suchas skin and lungs.

ExamplesAcidsAcetic acidHydrochloric acid

Nitric acid

BasesAmmoniumhydroxide

PotassiumhydroxideSodium hydroxide

HalogensBromineChlorineFlourine


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Practical Considerations

When dealing with corrosive materials in the field, itis imperative to determine:

How toxic is the corrosive material? Is it an irritant or does

it cause severe burns? What kind of structural damage does it do, and what other

hazards can it lead to? What protective equipment is needed to minimize

exposure? Are emergency flushing facilities or equipment nearby

(e.g., safety showers, eyewashes)? What specific handling procedures can be used to

minimize exposure?


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Reactives

A reactive material is onethat can undergo achemical reaction undercertain specified conditions.

The following are someexamples of reactivematerials:

Oxidants

Organic peroxides

Water reactives

Pyrophoric materials.


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Reactives

Oxidants

Organic Peroxides

Water Reactives

Pyrophoric Materials


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Organic Peroxides

Organic peroxides are a type of oxidizing substance that canbe shock/heat sensitive, flammable, and potentially explosive.

Examples are:

Benzoyl peroxide Methyl ethyl ketone peroxide Peroxyacetic acid.


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Water Reactives

These reactive materials are usually flammable solids that willreact in varying degrees with water or humid air.

Examples are:

Calcium carbide Metallic sodium.


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Pyrophoric Materials

These materials are capable of ignitingspontaneously when exposed to moist or dry air ator below 130 F.

They will also ignite in air at or below normal roomtemperatures in the absence of added heat, shock,or friction.

An example of a pyrophoric material is titaniumdichloride.


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Compressed Gases

A compressed gas refers to achemical which is typicallystored under pressure incylinders.

Compressed gases are oftenshipped and stored as liquids(under pressure at lowtemperature) or gases (underhigh pressure).

Compressed gases can be

flammable, corrosive, toxic,reactive or they may exhibitvarious combinations of thesetraits.


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BLEVE

A highly dangerous conditionwhich can occur when acontainer of liquified gas isexposed to a fire is known asBLEVE (boiling liquidexpanding vapor explosion).BLEVEs occur due tocontainer metal fatiguecombined with a tremendousincrease in pressure.

The container breakup can be

explosive, releasing contentsin an instant and rocketing thecontainer shell hundreds offeet.

Chemical


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ChemicalReactions/Compatibility

Understanding chemical reactions is important inprotecting yourself from the hazards they maypresent. Listed below are five characteristics ofchemical reactions.

Types

Exothermic/Endothermic

Incompatibility

Rate Compatibility

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Types

A chemical reaction is the interaction of two or moresubstances, resulting in chemical changes.

Chemical reactions usually occur in one of the following ways:

Combination: A + B -> AB Combination to either a more hazardous or innocuous

substance

Decomposition: AB -> A + B Breakdown to either a more hazardous or innocuous substance

Single Replacement: A + BC -> B + AC Double Replacement: AB + CD -> AD + CB


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Exothermic/Endothermic

Exothermic:

Exothermic chemical reactions give off heat andcan be the most dangerous.

Endothermic:

A separate source of heat is required to maintain

endothermic chemical reactions. Removing theheat source stops the reaction.


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IncompatibilityThe chart below lists hazards due to chemical reactions (incompatibilities).

Hazard Chemical Reaction Example

Generation of heat Acid and water

Fire Hydrogen sulfide and calciumhypochlorite

Explosion Picric acid and sodium hydroxideToxic gas or vapor production Sulfuric acid and plastic

Flammable gas or vapor production Acid and metal

Formation of a substance with greatertoxicity that the reactants

Chlorine and ammonia mixed togetherform the hazardous gas, chloramine

Pressurization of closed vessels Fire extinguisher

Solubilization of toxic substances Hydrochloric acid and chromium

Violent polymerization Ammonia and acrylonitrile, acrolein andwater


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Rate

The rate at which a chemical reactionoccurs depends on the following factors:

Surface area of reactants available at thereaction site - for example, a large chunk of coalis combustible but coal dust can be explosive

Physical state of reactant - solid, liquid, or gas Concentration of reactants

Temperature Pressure Presence of a catalyst.


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Compatibility

If two or more hazardous materials remain incontact indefinitely without reaction, they arecompatible.

Incompatibility, however, does not necessarilyindicate a hazard.

For example, dilute acids and bases can mix andneutralize each other to salts and water.

On the other hand, a strong acid and base mix canbe a hazard as it may react violently.


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Testing/Determination

The identity of unknown reactantsmust be determined by chemicalanalysis to establish compatibility.

Sometimes it is impossible toascertain the identity of a wastedue to time and money

constraints. In this event, simple tests must be

performed to determine the natureof the material or mixture.

Chemical test strips (SpilFyter),pH paper, and hazardcategorization (HazCat) kits canbe used to assist in classifying

and possibly identifyingunknowns.

Two varieties of HazCat kits exist;a wet chemistry type andcolorimetric detector tube-based.


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Test Your Knowledge

Which of the following corrosivesforms the greatest number of hydrogen

ions?

Acids

Halogens Bases


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Radiation Hazards

Radiation hazards are typicallyconsidered to be physical ratherthan chemical.

However, radioactive materialsmay exist in combination withhazardous chemicals as mixed or

special waste in a laboratory, at afacility or at a hazardous wastesite, so both hazardouscharacteristics must beconsidered.

A general overview of the hazardsof radiation is included here. Formore information on radiation

hazards, refer to your RadiationProtection Program.


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Radiation Hazards

Types of Radiation

Radiation Units

Detection andMeasurement

Biological Effects

Exposure Control

External Radiation


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Types of Radiation

Radiation exists in bothnatural and man-made forms.There are two generalcategories of radiation: Non-ionizing: Radiation that

imparts enough energy toremove electrons from oneorbital shell to another ofhigher energy (e.g.,microwaves, ultraviolet light)

Ionizing radiation: Radiationthat has sufficient energy toremove electrons from anatom (i.e., alpha and betaparticles, gamma X-rays).


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Radiation Units

The following are the mostcommonly used units ofradiation: Curie (Ci) is a special unit for

the activity of a substancewhich is measured in terms

of disintegrations per unittime

Roentgen (R) is a unit forexposure that gives thenumber of ionizations causedby photons in air

REM (Roentgen Equivalent inMan) is the special unit ofdose equivalent

RAD (Radiation AbsorbedDose) is a special unit ofabsorbed dose.

Radiation UnitsNameCurieRoentgen

Roentgen Equivalent in ManRadiation Absorbed Dose

SymbolCi

RREMRAD


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Detection and Measurement

Unlike many hazardoussubstances that possesscertain properties whichcan alert field personnel toover exposures, radiation

has no such warningproperties. Therefore, it is imperative

that properly maintained,calibrated, and operationalradiation survey meters

and dosimeters be utilizedwhenever radiation is aconcern.


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Biological Effects

Ionizing radiation causes primarilynonspecific damage to cells.Radiation passing through livingcells will directly ionize or exciteatoms and molecules in the cellstructure.

The total effect on cell processesis a function of the dose ofradiation.

The cell processes will be affectedin varying degrees: Some damage to the cell may be

repaired If the extent of the damage to an

organ is quite large, the organmay not be able to repair itself Cells may also begin to exhibit

uncontrolled growth.


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Exposure Control

Continuous monitoringusing survey instruments,pocket dosimeters andother survey equipment isneeded to assess externalradiation hazards.

The goal of radiationprotection is to establishexternal radiationprotection factors to reduce

exposure.

External Radiation


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Protection Factors

Time: Reducing the amount oftime in a radiation field reducesthe amount of exposure.

Distance: Increasing the distancebetween you and a radioactivematerial decreases the intensity of

the hazard. Shielding: The greater the mass

situated between you and aradioactive material, the lessradiation that will penetrate.

As Low As ReasonablyAchievable (ALARA): Keepingradiation exposure as low as

reasonably achievable can reduceunnecessary occupationalexposure.


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Test Your Knowledge

When you are exposed to radiation,you will know because:

Your eyes will begin to water.

You will not know.

You will feel respiratory discomfort.

You will smell fumes.


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Practical Considerations for Hazardous


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Practical Considerations for HazardousChemical Awareness

Know the chemicals and theirproperties.

Always consult MSDSs or otherreference sources.

Be aware of incompatibilities. Plan your work procedure. Be aware of the types of reactions

you can expect, especially whenother chemicals are introduced tothe process.

Know how to respond to anunexpected reaction: Stop work in progress Attempt to determine the cause,if it is safe to do so Consult an industrial hygienist orchemist.


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Test Your Knowledge

Which of the following is not a considerationwhen using hazardous chemicals?

Always consult an MSDS. Be aware of incompatibilities. Keep a glass of water in your work area in the

event that you get thirsty. Be aware of the types of reactions you can

expect. Plan your work procedure.


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Hazard Control Practices

The following safe work practices should always beused in hazard control: Handle materials carefully to prevent direct contact Limit exposure levels and time as much as possible

Enforce good hygiene practices Take appropriate fire prevention and control measures Use appropriate personal protective equipment Utilize equipment and tools not affected by the chemical

being handled Ensure that a chemical is not mixed with other chemicals

or substances which may result in adverse reactions Use engineering controls Use good common sense.


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Test Your Knowledge

Chemical hazard control practicesinclude the following:

Limit exposure time.

Use good hygiene.

Prevent contamination. All of the above.


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Summary

Measures you can take to minimize the risks associated withchemical hazard reactions include: Recognize chemical hazards, which are dependent on physical

properties, toxicity, use, and the environmental conditionspresent

Familiarize yourself with the chemical and physicalcharacteristics as well as the warning properties of chemicalhazards you may encounter during the course of your work

Be aware of the effect environmental factors may have onpotential hazards

Know hazard control and evaluation methods for the potentialhazards

Always consult MSDSs or other reference sources for moreinformation about chemical substances

Understand the multiple hazard rule Familiarize yourself with the various hazard classes.

chemical hazards and reactions

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