Environmental issues and hazards in the chemical research laboratory

Ulf Ellervik

Lecture 4: Accidental fires and explosions

Lecture 4 - outline

1. Introduction2. Fires3. Explosions4. Regulations5. Examples6. Incompatible chemicals

1. Introduction

• Flammable compounds are probably the most common hazardous material in thelaboratory• The hazard is dependent on the ability to vaporize,ignite and burn or explode

1. Introduction

• What are the dangers?

Solid flammable compounds -BH3•NEt3

Flammable liquids -ether

Flammable gases -acetylene

Self-igniting compounds -BuLi

Compounds that will form flammable -KHgases in contact with water

Oxidizing compound -KMnO4

Organic peroxides -benzoyl peroxide

Explosives -picric acid

1. Introduction• What is a fire?-combustion

CH4 + 2 O2 CO2 + 2 H2O

1. Introduction• What is a fire?fire, 1 mm/s

1. Introduction• What is a fire?fire, 1 mm/s

deflagration, 100 m/s

1. Introduction• What is a fire?fire, 1 mm/s

deflagration, 100 m/s

explosion, 1500 m/s

2. Fires2.1 Liquids

Flash point - the lowest temperature at which a liquid gives off vapor in sufficient concentration to be ignited by a flameIgnition temperature - the lowest temperature required to initiate combustion without a flameFlammability limits- the concentration of vapor in air where the mixture is flammable

2. Fires2.1 Liquids

2. Fires2.1 Liquids-Swedish regulations

Klass 1 tfp < 21°C Extremely flammable R12 F+ Highly flammable R11 F examples: acetone, ether, gasoline, pyridineKlass 2a 21°C < tfp < 30°C R10

examples: xylene, 1-butanol,

Klass 2b 30°C < tfp <55°C

examples: kerosene (fotogen), acetic acid

Klass 3 55°C < tfp < 100°C

examples: DMF, DMSO, nitrobenzene

2. Fires2.1 Liquids-Relative density of vapour

air 1.0toluene 3.2gasoline 3.0hydrogen 0.1

2. Fires2.1 Liquids-Statical electricity

Problem: -statical electricity in solvents can give a spark -example: relaxation time in heptan 0.18 s relaxation time in hexane: 2 days

Solution: -ground the container -do not pour from more than 10 cm

2. Fires2.2 Gases-Flammable gas - gas that is combustible in air at 20°C-Flammability limits (% in air)

0 25.0 50.0 75.0 100.0

Toluene

Silane

Propane

Methanol

Methane

Kerosine

Gasoline

Hydrogen

Ethanol

Ethane

Diethyl Ether

Carbon Monoxide

Carbon Disulfide

Ammonia

Acetylene

Acetone

Acetaldehyde

2. Fires2.3 Solid materialsDust explosions - suspensions of oxidizable particles in air can explode

2. Fires2.3 Solid materials

Metal fires - magnesium, sodium, aluminum, iron, zinc,dustMetal fires are very difficult to extinguish!

2. Fires2.4 Spontaneous ignition

A substance reaches its ignition temperature without an external heat source examples: oily rags, dust, organic material mixed with oxidizers, alkali metals, finely divided pyrophoric metals, white phosphorous

2. Fires2.5 Compounds that will form flammable

gases in contact with water

examples: sodium (hydrogen) lithium aluminum hydride (hydrogen) calcium carbide (acetylene)

2. Fires2.6 Different types of fires

Class A fires are ordinary materials like burning paper, lumber,cardboard, plastics etc.Class B fires involve flammable or combustible liquids such asgasoline, kerosene, and common organic solvents used in thelaboratory.Class C fires involve flammable gasesClass D fires involve combustible metals, such as magnesium,titanium, potassium and sodium as well as pyrophoric organometallicreagents such as alkyllithiums, Grignards and diethylzinc. Thesematerials burn at high temperatures and will react violently with water,air, and/or other chemicals.Class E (US: C) fires involve energized electrical equipment, such asappliances, switches, panel boxes, power tools, hot plates and stirrers.Water is usually a dangerous extinguishing medium for class C firesbecause of the risk of electrical shock unless a specialized water mistextinguisher is used.Class F (US: K) Cooking oil

2. Fires2.6 Different types of fires

An oil fire usually makes a lot of soot.

2. Fires2.6 Different types of fires

An oil fire usually makes a lot of soot.

2. Fires2.7 Extinguishers

Water extinguishers (usually not found in laboratories) are suitable for class A (paper, wood etc.) fires, but not for class B, C and D fires such as burning liquids, electrical fires or reactive metal fires. In these cases, the flames will be spread or the hazard made greater!Rather unusual!

Never ever use water on an oil fire!!!!

2. Fires2.8 Extinguishers

Foam extinguishers (usually not found in laboratories) are suitable for class A and B, but not D fires.

2. Fires2.8 Extinguishers

Dry chemical extinguishers are useful for class ABC and E fires andare your best all around choice. They have an advantage overCO2 extinguishers in that they leave a blanket of non-flammablematerial on the extinguished material which reduces thelikelihood of reignition. They also make a terrible mess -- but ifthe choice is a fire or a mess, take the mess! Note that there aretwo kinds of dry chemical extinguishers!Usually contain sodium bicarbonate or potassiumbicarbonate or ammonium phosphate, which also works on A fires.

2. Fires2.8 Extinguishers

CO2 (carbon dioxide) extinguishers are for class B fires. They don't work very well on class A fires because the material usually reignites. CO2 extinguishers have an advantage over dry chemical in that they leave behind no harmful residue. That makes carbon dioxide a good choice for an electrical fire involving a computer or other delicateinstrument. Note that CO2 is a bad choice for a flammable metal fires such as Grignard reagents, alkyllithiums and sodium metal because CO2 reacts with these materials. CO2 extinguishers are not approved for class D fires!

2. Fires2.8 Extinguishers

Sand. Do not forget sand for flammable metals (class D).

3. Explosions

3.1 Thermodynamics -How does an explosive work?

3. Explosions

energy

products

activation energy

explosionenergy

explosivecompound

3.1 Thermodynamics -How much energy?

3. Explosions

Combustion with lot of air

3 CO2 + 2.5 H2O + 1.5 N2 + 0.5 O

7 CO2 + 2.5 H2O + 1.5 N2 – 10.5 O

O2NO ONO2

ONO2

NO2O2N

NO2

3.1 Thermodynamics -How much energy?

3. Explosions

The Kistiakowsky Wilson rules- hydrogen is converted to water-if there is oxygen left carbon is converted to CO-if there is oxygen left CO is converted to CO2-nitrogen is converted to N2

3.5 CO + 3.5 C + 2.5 H2O + 1.5 N2

NO2O2N

NO2

3.1 Thermodynamics -Explosion power = explosion energy x gas formation

3. Explosions

3.1 Thermodynamics -Explosion power = explosion energy x gas formation

3. Explosions

3.2 Common explosivesA compound is may be explosive if it contains a lot of oxygen and some of the following groups

3. Explosions

peroxides and ozonides

chlorates and perchlorates

nitrocompounds and nitrates

diazocompounds and azides

acetylenides

fulminates

organometallics

–OClO2 –OClO3

–NO2 –ONO2

–N –N3

–O–O– –O–O–O–

–C C–

N–

–ONC

M–C

3.2 Common explosives

3. Explosions

PbN6Hg(ONC)2O2NO ONO2

ONO2

NO2O2N

NO2

OHNO2O2N

NO2

NN

NNO2

NO2O2N

Explosive explosion

energy (kJ/mol)

gas formation (dm3/g)

explosion power (%)

aktivation energi (kJ/mol)

mercury fulminat

–500 0.21 14 105

lead azid –469 0.22 13 160 nitroglycerin –1406 0.74 171 176 pikric acid –744 0.83 100 242 TNT –1016 0.74 115 222 RDX –1118 0.91 169 199

3.3 Organic peroxides

3. Explosions

Some compounds can form organic peroxides due to airoxidation

List A - (Three Months) - Peroxide Hazard on StorageDivinyl acetyleneIsopropyl etherPotassium metalSodium amideVinylidene chloride

3.3 Organic peroxides

3. Explosions

List B - (Twelve Months) - Peroxide Hazard on ConcentrationAcetalCumeneCyclohexeneDiacetyleneDicyclopentadiene t-butylalcoholDioxaneEthylene glycol dimethyl ether (glyme)Ethyl etherMethyl acetyleneMethylcyclopentaneMethyl i-butyl ketoneTetrahydrofuranTetrahydronophthaleneVinyl ethers

3.3 Organic peroxides

3. Explosions

OO

OOO

O

triacetoncykloperoxid, TATPWARNING! Too unstable to

be used as an explosive

4.1 Labelling of flammable compounds

Swedish regulations:

Brandfarliga varor = Brandfarliga vätskor Brandfarliga gaser Brandreaktiva varor

4. Regulations

4.1 Labelling of flammable compounds

Swedish regulations:

Gases:

4. Regulations

4.1 Labelling of flammable compounds

Swedish regulations:

Flammable liquids

4. Regulations

4.1 Labelling of flammable compounds

Swedish regulations:

Fire reactive compounds

4. Regulations

orand

4.1 Labelling of flammable compounds

Swedish regulations:

Flammable compounds may not be stored with toxic compounds or corrosives!

4. Regulations

4.2 Electrical installations

Swedish regulations:

Classification of zones for flammable materials

Zone 0 - allways risk for explosion, inside containers

Zone 1 - Som,etimes risk for explsion, 0.5 m from an open bottle

Zone 2 - seldom risk for explosion, 1 m from an open bottle

4. Regulations

5. Examples

Acetylene - explosive in 2.5-80% in air, dangerous underpressureAlCl3 -forms large amount of HCl if subjected to waterAmmonia -reacts with iodine to give explosive nitrogentriiodideBenzoyl peroxide - decomposes spontaneously above50°CCarbon disulfide - toxic and can be ignited on a glowinglight bulbDiazomethane - extreme explosion hazardDMSO - decomposes violently on contact with activechlorine compounds

5. Examples

Dry ice - do not keep in closed containerEthers - peroxide hazardEthylene oxide - can explode if heatedHalogenated compounds - do not mix with sodiumHydrogen peroxide - can decompose if in contact withiron or other metalsLitium aluminum hydride - can take fire withtetrahydrofuran

5. Examples

Ozone - give highly explosive ozonidesPalladium - can get on fire when dryPerchlorates - the use should be avoided.Permanganates - explosive if mixed with sulfuric acidPhosphorus - should be stored under waterPhosphorus trichloride - reacts with water to givephosphorus acid which decomposes and form phosphinewhich may ignitePotassium - more reactive than sodium

6. Incompatible chemicals