Gas tester

GAS TESTER HL

YOUR ENVIRONMENT,YOUR SAFETY, LET ’S MASTER THEM TOGETHER

By Mike MartindaleNews Staff Writer

MENOMENEE, Mich. –Bill Hofer was the first to

collapse in the dark manure pit. Inhaling a combination of

toxic gases, he quickly lost consciousness and slipped down into the pool of murky liquid in the bottom of the 12-foot hole.

Then one after another, the four men at the top of the pit scrambled in, trying first to save Hofer, and then each other, from the deadly fumes.

Within five minutes all were dead or dying in what is believed to be the worst farm accident in Michigan history.

Killed yesterday along with the 63-year-old Hofer were his

uncle, Carl

Theuerkauf, Sr., the 65-year old patriarch of the centennial farm; two of Theuerkauf’s sons, 37-year old Carl Jr. and 28-year old Tom; and Carl Jr.’s 15-year old son, Daniel.

“I’m sure that when one person slipped or fell, out of love and for help, one after another went in,” said Richard Breyer with the county farm extension service in Menominee.

Dorothy Theuerkauf, who lost a husband, two sons, and a grandson in the tragedy said: “I can’t believe something like this could happen. It will probably take me a couple of weeks before it actually sinks in.” On Thursday, investigators said the five men were using a

pump to empty a partially covered, 12-foot deep concrete

manure pit, and were almost finished when the pump

clogged. Hofer descended into the

darkness to clear the block.“It’s unknown which one

went in next, but eventually they all went in to save the rest,” said Menominee County Sheriffs Deputy Booth Whipp.

County Medical Examiner Dr. Paul Haupt estimates it took about 90 seconds for each of the men to suffocate in the invisible

cloud of gas, composed primarily of methane and

hydrogen sulfide.

5 died trying to save each other

65% of fatalities due to atmospheric hazards

Ref. # Accident Type Events Injuries Deaths

1 Atmospheric condition in CS 80 72 78 2 Explosion or fire in CS 15 49 15 3 Explosion or fire at point of entry 23 20 32 4 Electrical shock or electrocution 11 2 9 5 Caught in / crushed by machinery 10 3 10 6 Engulfment 16 0 16 7 Struck by falling objects 15 15 0 8 Falls inside Confined Space 27 26 1 9 Ingress / egress 33 30 3 10 Insufficient maneuverability 15 15 0 11 Eye injury 10 10 9 12 Other 21 6 15

----------------------------------------------- Total 276 234 193

Miner’s Canary

Japanese Waltzing Mouse

Flame Safety Lamp

The risks incurred:

•The explosion (EX)

•The poisoning (Tox)•The suffocation (O2)

EXPLOSIONRISKS

3 parameters for an EXPLOSION

• Requirement for an explosion: the ignition triangle

Always present in the air

Oxidiser(Oxygen: approximately 21% of air)

Ignition Source1) Electric arcs or sparks2) Frictional heating & sparking3) Hot surfaces4) Static Electricity

Fuel1) Flammable gases & vapours

(eg Methane)2) Combustible dusts

(eg Coal dust)

IGNITION TEMPERATURE...

• It is the temperature from which a product starts spontaneously its combustion without the intervention of an outside source (spark).

• H2 : 560°C• CH4 : 550°C

FLASH POINT…(FLP)

• It is the minimal temperature from which a mixing of vapours, issued from liquids and air, may inflame in normal conditions of pressure.

• gas oil : + 55°C

About explosive atmosphere...About explosive atmosphere...

• For each combustible gas or vapour in usual conditions of given temperature and pressure, there are:

• a LOW EXPLOSIVE LIMIT : LEL

• an UPPER EXPLOSIVE LIMIT :

UEL

Combustible gases

• LEL :

lowerexplosive

limit

• The minimum concentration of gas or vapor mixed with air that will cause an explosion when its comes in contact with an ignition source.

Combustible gases

• UEL :

upperexplosive

limit

• The maximum concentration of gas or vapor mixed with air that will cause an explosion when it comes in contact with a ignition source.

AIR/GAS CONCENTRATIONS

100% air

explosive richlean

0% 100% of LEL

LEL5% volume UEL14.7% volume

Alarm at 20% of LEL (100 % gas)

a NEW directive for EUROPE !

Potentially EXplosive ATmospheres

ATEX DIRECTIVES

• 94/9/CE ( manufacturers’ directive) = European instruments using

• 1999/92/CE ( workers’ directive) = employees protection:

• annexe I:types of zones• annexe II:categories of instruments for each zone.

NEW DIRECTIVES ATEX...• Since July 2003, it has

been mandatory that all equipment with a potential source of ignition which is being sold on the european market for the first time is accompagnied by a declaration of conformity to the ATEX product Directive 94/9/EC.

• Since july 2003, it has been mandatory that all new installations (and modifications to existing installations) should meet the requirements of the ATEX User directive 1999/92/EC.

NEW DIRECTIVES ATEX...

• By July 2006, all plants within Europe should be able to demonstrate full compliance with the requirements of 1999/92/EC as adopted in each member state.

• In the UK this is « the dangerous substances and explosive atmospheres regulations » : DSEAR.

NEW DIRECTIVE ATEX...www.ne

wappr

oach

.org

Or : w

ww.iner

is.fr

Or: europa.eu.int/comm/enterprise/atex/index.htm

The new directive ATEX (01/07/2003)

• Requires in short:• a certification delivered by a notified laboratory

• CE marking to be affixed to all electrical and electronic instruments marketed in EUROPEAN UNION MEMBER STATES(The CE marking guarantees that the instrument conforms to applicable electromagnetic radiation and immunity requirements).

• Compliance is mandatory,which means you must ensure that your products meet all of the directive’s requirements.

List of European Standard

relevant to Performance Requirements ( additional standard to Explosion Protection i, d, e , m, etc ) and mandatory for safety

relevant devices according article 1.5 de l’Annex II de la Directive Atex 94/9/CE

EN 61779-1 ( replace EN 50054 ). Performance requirements of Electrical apparatus for the detection and measurement of flammable gases - Part 1: General requirements and test methods

EN 61779-2 ( replace EN 50055 ) : Performance requirements for group I apparatus indicating a volume fraction up to 5 % methane in air .

- EN 61779-3 ( replace EN 50056) : Performance requirements for group I apparatus indicating a volume fraction up to 100 % methane in air .

EN 61779-4 ( replace EN 50057) : Performance requirements for group II apparatus indicating a volume fraction up to 100% lower explosive limit. .

- EN 61779-5 ( replace EN 50058) : Performance requirements for group II apparatus indicating a volume fraction up to 100% volume. .


EN 50104: Electrical apparatus for the detection and measurement of oxygen – Performance requirements and test methods.

EN 50270: Electromagnetic compatibility - Electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen

EN 50271: Electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen - Requirements and tests for apparatus using software and/or digital technologies.


EN 45544-1 : Workplace atmospheres - Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours -- Part 1: General requirements and test methods

EN 45544-2 :Workplace atmospheres - Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours -- Part 2: Performance requirements for apparatus used for measuring concentrations in the region of limit

List of European Standard relevant to Performance Requirements not mandatory, eg not yet in the Atex list for harmonised standard

EN 45544-3 : Workplace atmospheres - Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours -- Part 3: Performance requirements for apparatus used for measuring concentrations well above limit values

EN 45544-4 :Workplace atmospheres - Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours -- Part 4: Guide for selection, installation, use and maintenance

List of European Standard relevant to Performance Requirements not mandatory, eg not yet in the Atex list for harmonised standard

The new directive ATEX (01/07/2003):continued...

• Safety systems fail safe application. • GAS or DUST hazardous areas indication

(marking)• production quality assurance• product verification• conformity to type tests carried out under

the responsability of notified organisme.

ATEX / CENELEC: marking

• Until July 2003, a new marking:

CENELEC T° Class

europ Directives. organism exploINSTRUMENT Group

categorygas

cenelec protectionClass gas

T° Class

PROTECTION MODE

GAS GROUP

CE MARKING exampleCE MARKING example

• The certified equipment must carry a plate indicating :-the name and address of the manufacturer

-designation of the type of equipment-CE marking followed by the identification number of the organism where such body is involved in the production control stage:CE xxxx

-the serial number of the equipment- year of construction

-specific marking followed by group II for group II,2 for category 2 and G for gas

- complementary marking:EEx d IIB T4 INERIS xxATEXxxxx X

What is an HAZARDOUS AREA as per ATEX

1999/92/CE:annexe I ?

ATEX 1999/92/CE• New directive ATEX concerning the

instruments in hazardous areas and mines “group I”:

• the whole concentrations: M1• above a limit value: M2

ATEX 1999/92/CE:ZONES

• New directive ATEX concerning the instruments in hazardous areas and surface industries “group II” distinguishes the next groups of zones:

• Zone 0 G (gas) and zone 20 D (dusts)



ZONE 0G /20 D ATEX probability = very high

• Where ignitable concentrations of flammable gases, vapours, liquids or dusts can exist all of the time or some of the time and for a long time under normal operating conditions .required

equipment (annexe II):category 1= ia only !

intrinsic Safety

ZONE 1G/21D ATEX probability = high • Where ignitable concentrations of

flammable gases, vapours,liquids or dusts can exist some of the time under normal operating conditions.

• required equipment (annexe II):category 2 = d or is or e .

ZONE 2G/22D ATEX probability = low

• Where ignitable concentrations of flammable gases, vapours,liquids or dusts are not likely to exist under normal operating conditions.

• Required equipment (annexe II):category 3 (minimum protection).

DANGEROUS ZONE:example

• In accordance with the new regulation ATEX:

CATEGORY 3

CATEGORY 2

CATEGORY 1

Required equipment

GAS and EQUIPMENT

CLASSIFICATION.

Explosion groupsExplosion groups• The IEC and the CENELEC

(European committee of electrotechnics normalisation) drew up a classification of flammable products :

• the I group only concerns the equipment used in firedamp mines.

• the IIB group includes all gases except hydrogen, acetylene, carbon sulphide and nitrile of ethyl

• the IIC group includes all gases and vapours.

classification of temperatures

• "T" followed by the number from 1 to 6 indicates the class of the maximum temperature of surface that can bear the device, taking care of a security’s coefficient : no surface of the equipment in contact with the gas/air mixture should exceed the MIT of the gas.

• Each flammable gas or vapour has a specific Minimum Ignition Temperature.

• This classification is relevant to a given surrounding temperature ( 40°C).

classification of temperatures

• Example:T6

Internalfault

85°Cmax

Gasdetector-casing Gas detected

ignition T° >85°C

Temperature classes

IECCENELEC

(group II)

temperaturemaximum

of surface

T6 T5 T4 T3 T2 T1

85°C 100°C 135°C 200°C 300°C 450°C

• To ease the selection of equipment, six different temperature classes have been created for both gases and equipment.

Function of Explosion protection

• The function of the discipline of explosion prevention is to ensure that there is a negligible probability that a means of ignition and any significant quantity of a potentially explosive atmosphere can occur in the same location at the same time.

• Both mechanical and electrical methods are imployed and have been classified under 4 categories:

4 categories of protection• Non-incendive equipment (comparable with n)

(EN 50021)• Flameproof or explosion-proof equipment

(d) (EN 50018)

• intrinsic safety equipment (i) (EN 50020)• increased safety equipment(e)(EN 50019)

NON-INCENDIVE EQUIPMENT(n)

• Transmitters « n » for zones 2 (gas) and 22(dusts)

• In accordance with regulation CEI 79-15: minimum protection (non sparking)

• Typical applications:instrumentation, control gear, electronic systems, measurement and control.

FLAMEPROOF or explosion-proof equipment (d)= containment

• Elements sensitive to produce a spark are enclosed in casings resistant to an eventual internal explosion.

• This material is in accordance with the decree of March 28, 1960:

FLAME PROOF TRANSMITTERS:spécifications of installation

• Transmitters « d » for zones 1 and 2(gas) and 21 and 22(dusts)

• The cable will be mecanicly protected• Transmitter ’s body will be connected to the earth• If connections are in classified area:made in

certified housing.• Typical applications: switch gear, motors , pumps.

equipment with intrinsicequipment with intrinsicsafety (i) = prevention of ignitionsafety (i) = prevention of ignition

• Intrinsic safety aims to limit the level of energy release under any circumstances ( MIE !…..)

• It is the ideal equipment in particular in an atmosphere with hydrogen.

INTRINSIC SAFETY:FAULT CONDITIONS

• The definition of intrinsic safety includes reference to fault conditions.

• Two categories of intrinsically safe instrument are defined in the standards: ia and ib.

• The categories differ in two principal respects:- the number of specified faults which the instrument

can sustain without producing a risk of ignition- the values of the safety factor which are applied to

the ignition data used in the design...


• Category « ia »:• instruments of this category must be incapable of

causing ignition in normal operation or with a single fault or with any two independent faults. A safety factor of 1.5 must be applied to relevant ignition data for normal operation or for a single fault and a safety factor of 1.0 for the two-fault condition.

• Intrinsic safety category « ia » is the only method of protection approved for zone « 0 or 20 ».


• Category « ib »:• instruments of this category must be incapable of

causing ignition in normal operation or with a single fault . A safety factor of 1.5 must be applied to relevant ignition data for normal operation or

for a single fault.

• Intrinsic safety category « ib » is generally approved for zone « 1 or 21 ».

Intrinsic safetyIntrinsic safety TRANSMITTERS:spécifications of installation

• Transmitters for zones 0,1 or 2(gas) and 20,21 and 22(dusts)

• Obligatory powered by an intrinsic source:28V/300 ohms

• If connections are in classified area:made in certified housing.

• Typical applications: instrumentation, control gear, electronic systems, measurement and control.

Intrinsically-Safe Systems

I.S. systems require installation of power-limiting barriersBarriers will ground the system power supply

Ground-fault monitoring systems are incompatible

equipment with increased safety (e)

• Transmitters « e » for zones 1 and 2(gas) and 21 and 22(dusts).

• This material is realised so that the occurrence of accidental sparks is highly improbable

• protection by insulator : the whole equipment is dipped in a resin or a liquid to be totally separated from the ambient atmosphere.

equipment with increased safety spécifications of installation

• Transmitters « e » for zones 1 and 2(gas) and 21 and 22(dusts)

• The cable will be mechanically protected• Transmitter ’s body will be connected to the

earth• If connections are in classified area:made in

certified housing.• Typical applications: motors, light fittings.

Types of protection:symbols and zones

Non-incendiveNon-incendiveimmersionin oilinternal under pressure

pulverulentfilling

flameproofcasing

increased safety

intrinsic safety

nnOOppqdei(a/b)

OG/20D 1G/21D 2G/22D

X

X XX X

X(« a » only) X X

Type of PROTECTION

Index of protection

• Dust, water and impacts damage the equipment. Device’s casing is protected against this outside parameters.

• So the IEC defined a list of different degrees of protection and a numeration

Degree of protectionIP xxx = degree of protection of casings of electric equipment

against solids against liquidsagainst liquids mechanical protectionmechanical protection

0

1

2

3

4

5

6

no special protection

larger than 50 mm.

larger than 12 mm.

larger than 2,5 mm.

larger than 1 mm.

Dust- tight

0

1

2

3

4

5

6

7

8

No special protection

dripping waterdripping water falling vertically any angle up to 15°

rain falling vertically any angle up to 60°

splashing water, splashed from any direction

water projected from a nozzle againstthe equipment from any direction

heavy seas or powerfulwater jets immersion under definedconditions

submersion

0

1

2

3

5

7

9

No special protection

Impact energy = 0,225 joule

Impact energy= 0,375 joule

Impact energy= 0,5 joule

Impact energy= 2 joules

Impact energy = 6 joules

Impact energy = 20 joules

Dust protected

Protected against

POISONING RISKS

Where can we be poisoned ?

• In every place where these toxic products are:used,manufactured,transformed,stored

• Examples of toxic gas emission sources :• Combustion (CO/NO/NO2/SO2)• Incineration (H2S/NH3/HCL)• Fermentation (H2S/NH3)

Example:toxicity caused by carbon monoxide in terms of time and concentration

Time in a toxic atmosphere

00,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,16

1 2 3 4 Hours

carbon

mon

oxide

concent

rati

onii

na

atmosphere

Death

In danger of death

Headache and nauseaPerceptible effect

No perceptible effect

% CO% COin the airin the air

4 hours4 hours

Concept of LIMIT VALUES

• The Short Term Exposure Limit: STEL

• Time-weighted average: TWA

• Gases and vapours limit values are in volume (ppm:part per million).

STEL• The STEL is admitted value for the

medium in time, concentrations in which a worker is exposed for less than 15 minutes:

• SUBSTANCES with IMMEDIATE EFFECTS.

TWA

• TWA : the average concentration of contaminants over a specified time period (8 hours : 5 days a week):• SUBSTANCES with main CUMULATIVE

EFFECTS

Effects of carbon monoxide (CO) exposure

ppm level* effects time35 Max. permissible level 8 hours200 Slight headache 3 hours400-600 Headache, disconfort 1-2 hour1000-2000 Staggering,heart

palpitation 1.5 hour2000 à 5000 Unconsciousness, death 0.5 – 1 hour

*values are approximate

CO has an affinity for human blood hemoglobin that is over 200 times greater than oxygene.

Toxic risks :generations

RISKS WITH

RISKS WITH

OXYGEN

OXYGEN

Risks with OXYGEN

• The oxygen is essential for the life, it represents 20.9 % of the air that we breathe.

• A deficiency of oxygen is as important as an oxygen enrichment, each variation will provoke important effects on human beings.

Effects of OXYGEN :

• 20.9 % --> Normal concentration

• 19 % ---> tiredness and yawn...• 14 % ---> pulse up, impaired co-ordination, perception and

judgement...• 10 % ---> Nausea, mental failure, fainting,

unconsciousness, ashen face, blueness of lips, and vomiting• 8 % ---> Coma in 40 seconds, convulsions, respiration ceases,

death

• 3-5 % ---> life expectancy; 3-5 minutes.

An oxygen deficiency in confined spaces can be explained by:

• A defect of the ventilation system or a lack of ventilation

• the presence of another gas in full quantity (accidental leak)

• an oxygen consumption during a chemical reaction such as combustion

• Inertion

Where are you exposed ?Confined areas:

• Soldering and cleaning of tanks

• Reparation of furnaces• Visit of inert stocking

• Penetration in silos• Premises without

ventilation

In the trenches, the low places:

• in research of leak• in visit of control

• in the cellars and the sewers...

A moderate oxygen enrichment:

• can however cause accidents

• It provokes an EUPHORIA causing a modification of the sense of DANGER and vision !

Effects of OXYGEN:

• > 22 % ---> euphoria, modification of the sense of danger and vision = maximum safe level (OSHA)

• < 22 % --> no respiratory troubles,

• 20.9 % --> oxygen content in “AIR”

PROCESSES using OXYGEN

• For its energetic properties:• During combustion, to have more calories or a

higher T° than air…• In oxypropane, oxyacetylene flames,examples of

applications:- welding, soldering, surface hardening, forming

- stripping, flame spray coating- oxycutting

- iron and steel industry, foundry, glassworks burners- blast enrichment in blast furnaces.

PROCESSES using OXYGEN

• For its oxidant properties:• in the iron and steel industry, it ’s used in pure

oxygen converters, to refine cast iron and steel• in non-ferrous metal metallurgy, it ’s used to

refine copper, roast sulfurous ores, assay carbon in metals

• in the paper industry, to bleach paper pulp.

Functional Safety and Safety

Integrity Level SILThe Standards EN 61511 - EN

61508 – EN 50402Application to Gas detectors

GAS ANALYSIS GAS ANALYSIS METHODSMETHODS

Catalytic sensorCatalytic sensor

The catalytic sensor, also referred to as the catalytic bead sensor, is commonly used to detect and

measure combustible gases from 0-100%LEL.

AIR

9

Example of CombustionMethane (Natural Gas)

0% 100 %by volume

9


100 % LEL or 5% by volume“Same Thing”

LLEELL

AIR

0% 100 %by volume

9



15% by volume

AIRLLEELL

Explosive Mixture

0% 100 %by volume

UELUELToo Rich to BurnToo Rich to Burn

9


15% by volume

Explosive Mixture


LLEELL

0% 100 %by volume

Common Combustibles

LEL UEL Methane 5.0% 15% by volume Hydrogen 4.0% 75% Acetylene 2.5% 100% Propane 2.1% 9.5% Butane 1.9% 8.5% Pentane 1.4% 7.8% Hexane 1.2% 7.5%

A combustible hazard exists whenever readings exceed

10% LEL

Not 20%

Catalytic sensorsCatalytic sensors• The sensor is composed by two

platinium spirals, both plated with a ceramic coating (alumina)

• one of the pellistor is soaked with a special palladium catalyst that causes oxidation : detector (sensing bead)

• while the other one is not treated in order to forbid oxidation : compensator ( reference element).

• Those two filaments and their supports are fixed in a « flameproof » body of cell.

Flame arrestor

Physical principle : Wheaststone bridge

• The working principle of these sensors is based on flammable gas oxidation on the surface of a catalytic element with electric heating

• The current passes through the spirals in order to reach 450°C temperature that allows gas oxidation

• when fuel gas has burned in the detector, oxydation causes a temperature increase only in the treated pellistor and not in the non-treated one ( reference), causing unbalance in the bridge circuit.

Balanced Wheatstone Bridge

V2

V1

Fixed Resistor

Fixed Resistor Active Bead

VOUT

Reference Bead

15 % O2 mini

mV

Combustible sensors detect gas by catalytic combustion

Stainless steel housing

Mounting

Flame proof stainless steel sinter

Three wire connection

Matched pair of pellistor beads

PTFE Mounting Disc

PCB Board

PELLISTOR HEADER DETAIL

Catalytic Combustion Response

Catalytic sensors : typical response curve

SUP

?

CATALYSE : note

• Flammable gas oxidation: must be used in environments containing

a concentration of oxygene (O2) > 15% .

Catalytic Gas Sensors: ... Note !• The sensor can be poisoned so that it cannot

respond to a flammable gas if exposed to lead, silicone or certain other gases…

• The presence of inhibitors or poisons is the most common cause of problems in gas detection systems and, for this reason, it ’s necessary to pay attention in order to avoid any contamination.

Catalytic Gas Sensor Poisons/Inhibitors

• Inhibitors ( H2S, SO2, halogenated compounds) causes a temporary sensitivity loss of the sensor

• Poisons affect catalytic sensor response & longevity and cause a permanent reduction of the sensor sensitivity that may be completely damaged

• Erosion, impervious covering, or plugging active sites• Impact depends on poison type, level, time of exposure• Known catalytic sensor poisons:

– silicone oils, greases, resins (RTV adhesive)– halogens ( halon, chlorine, fluorine, bromine, freon)– phosphate esters– tetraethyl lead, trichlorobenzene– acid and pvc vapors, other corrosive materials …

ADVANTAGESADVANTAGES

• The principle is simple, it uses a real phenomenon

• valid for all flammable gases• very short response time ( <15s.)• very good repeatability• very good reproducibility• low cost

The thermal conductivity sensor

Has been used in instruments for measuring gases above the %LEL

range and for leak detection.

Thermal conductivity

• Measuring the thermal conductivity of gases was one of the earliest forms of gas detection and it ’s suitable for % volume levels of certain binary mixtures : two different gases, one of which can be air .

• TC gas detectors operate by comparing the thermal conductivity of the sample with that of a reference gas ( usually air)• this principle of detection , without chemical reaction,

can be used in an atmosphere with or without oxygene.

Thermal conductivity : principle

• The sensor consists of two elements, both comprised of a wire coil.One element (detector) is exposed to the atmosphere, whereas the other element (reference) is sealed in a standard gas atmosphere such as nitrogen or air.

Air + gas

airHousing of cell D

C

Thermal conductivity : principle

• The reference element compensates for changes in temperature.

• The elements are heated to an operating t° of approximately 250°C.

ADVANTAGESADVANTAGES• High concentrations measurement ( 100% v/v)• With or without oxygene • possibility of detection: helium ….• No poisonning• long life time • resistant filaments.

Limitations of use

• This technique is only suitable for gases and vapours whose thermal conductivity is significantly different from air !

• Thermal conductivity sensors are used primarily in portable gas leak detectors.

INFRARED ABSORPTION

TCOD IR (CO2)

OLCT IR

INFRARED SENSORS :

• The non-dispersive infrared sensor, commonly referred as the infrared sensor, is based on the principle that gases absorb light energy at a specific wavelength, typically in the infrared range.

INFRARED SENSORS

• Gases that contain more than one type of atom absorb infrared radiation.

• Gases such as carbon dioxide (CO2), carbon monoxide (CO), methane (CH4) and sulphur dioxide (SO2) can be detected by this means …

• But gases such as oxygen (O2), hydrogen (H2), helium and chlorine (CL2) cannot.

INFRARED ABSORPTION

Emitter

IR Source

c

Receiver

( filament / semi-conductoror laser)

Optical

filter

Measurement path lenght•When flammable gas passes between the source and detector, the gas

absorbs infrared radiation and a lower intensity is registered at the detector

•The gas concentration is directly proportional to the amount of energy absorbed and this absorption is illustrated by the BEER LAMBERT

formula.

ADVANTAGES in ADVANTAGES in summarysummary

• Instantaneous response time• no poisoning• no need of oxygen• no interferent gases

Limitations of use

• Exposure to high concentrations may saturate the instrument for a finite time.

• Cannot detect monatomic or diatomic homonuclear molecules : mercury, chlorine and other halogens ...

C1100

Typical measurement tasks

• Combustion efficiency monitoring : CO/CO2• Continous Emission monitoring systems:

CO/CO2/SO2 and helium• Process control: CO/CO2 and total hydrocarbons• Landfill gas monitoring : CH4/CO2• Plant protection: CH4/C3H8/C4H10• Distilleries and breweries : CO2• Personnal protection : CO2• Automotive emissions.

SEMI-CONDUCTORS

SEMI-CONDUCTORS

Heater Control

Platinum Coil Heater

Collector

Schematic Diagram of a Bead-type Sensor•This semi-conductor (SNO2 for example) is placed on the surface of a substratum

(tube or plate).A

PRINCIPLE

• A filament is heated by an electric current,• the substratum increases its temperature

until it reaches 300 to 500 °C.• The sensitivity of SnO2 to different gases

varies with the temperature.• This temperature will be chosen to work

with the maximum operation sensitivity.

• Signal= induced variations of electric conductivity,

by absorption of gas, on the surface of a metallic oxide.

When gas enters the sensor it reacts with the oxide coating which causes a decrease in resistance between the two

electrodes.

PRINCIPLE

Detected GASES

• Toxic and flammable gases: VOC , hydrocarbures (toluène,xylène …), vapors of hydrocarbures (essence,kérosène…), cétones (2-butanone…), esters, (acétate of méthyle, éthyle éther…), alcools (méthanol…)

• FREONS.• example : toxic products with low concentrations,

ADVANTAGESADVANTAGES

• High sensitivity • very good stability of the signal• long life time (~ 5 years)• low cost

• used to measure a wide range of gases and vapours.

• Commonly used in low cost, hard-wired gas detection systems

Limitations of use• Wide range of sensitivity (interference) to different

gases• after exposure to high gas concentrations the sensor

may need a recovery time of several hours and may have irreversible changes to its zero gas reading and sensitivity

• exposure to basic or acidic compounds, silicones, organo-lead, sulphur compounds and halogenated compounds may have a significant effect on sensitivity

• Oxygen concentration,humidity and temperature may have a significant effect on sensitivity.

Electrochemical gas sensors

with liquid or gelled electrolyte.

Threshold Limit Value (TLV)

• Determined by American Conference of Governmental Industrial Hygienists (ACGIH)

• Guidelines for control of potential health hazards

• Intended as recommendation

Permissible Exposure Limit

(PEL)• Determined by OSHA

• Sets limits for legal unprotected worker exposure to a listed toxic substance

• Force of law!

• Given in “Parts-per-Million” (ppm) concentrations– 1 % = 10,000 ppm

OSHA Permissible Exposure Limits are defined

in three ways:• Time Weighted Average (TWA)

• Ceiling

• Short Term Exposure Limit (STEL)

TWA is projected value

• When monitoring session less than eight hours, TWA projected for the full eight hour shift.

• When monitoring session more than 8 hours, TWA calculated on an “equivalent” 8 hour shift basis

Ceiling Limit• Ceiling is the maximum concentration

to which an unprotected worker may be exposed

• Ceiling concentration should never be exceeded even for an instant

Short Term Exposure Limit

(STEL)• Some gases and vapors have an

allowable maximum Short Term Exposure Limit which is higher than the 8 hour TWA

• STEL values are calculated as 15 minute time weighted averages

STEL vs. TWA and Ceiling

TWA

Ceiling

STEL

15 min.

Toxic effects H2S1 PPM Smell

10 PPM 8 hr. TWA15 PPM 15 min. STEL

100 PPM Loss of smell300 PPM Loss of consciousness with time

~( 30 min).1000 PPM Immediate respiratory arrest, loss of

consciousness, followed by death

Substance Specific Toxic

Sensors

• Gas diffusing into sensor reacts at surface of the sensing electrode

• Sensing electrode made to catalyze a specific reaction

• Use of selective external filters further limits cross sensitivity

Electrochemical gas sensors

• Are widely used for the gas detection of toxic gases at the ppm level and for oxygen in levels of % of volume .

Electrochemical Toxic Sensor

Capillary diffusion barrier

Metal housing

Reference electrode

Counter electrode

Electrolyte reservoir

Electrode contacts

Sensing electrode

Toxic electrochemical sensors

In summary …In summary …• This method is based on the

measurement of the current established between a sensing

electrode and a counter electrode.• A reference electrode is often used

to stabilize the measurement.• Gases react electrochemically to

the sensing electrode: gases are reduced or oxidised.

Oxygen electrochemical sensors

• There are two fundamental variations in fuel-cell oxygen sensor designs:

• Partial atmospheric pressure, is that fraction of the total atmospheric pressure due to oxygen

• Capillary-pore, these sensors are much less influenced by changes in presure than partial pressure oxygen sensor designs.

Mechanisms of oxygen sensor failure

• Oxygen sensors may be affected by prolonged exposure to acid gases

• Such as carbon dioxide (CO2)• Most oxygen sensors should not be used

continuously in atmospheres containing more than 25%CO2

• Limitation of operations in extrem cold or excessivily hot temperatures…

Oxygen enters the sensor through a

capillary poreOxygen is reduced to hydroxyl ions at the cathode:O2 + 2H 2

O + 4e- 4OH-Hydroxyl ions oxidize the (lead) anode:

2PB + 4OH- 2PbO + 2H 2 O + 4e-

Overall cell reaction:2PB + O 2 2PbO

Oxygen Sensor

4 e-

Electrolyte

Cathode

Anode

Oxygen

Load Resistor

Diffusion barrier

O2 Sensor Failure Mechanisms

• Failure modes which lead to lower current output:

– All available surface area of Pb anode converted to PbO2

– Electrolyte poisoned by exposure to contaminants

– Electrolyte leakage

– Desiccation

– Blockage of capillary pore

PID Sensor Technology

A PID sensor works differently than other sensors and often used in situations where high sensitivity (sub-ppm levels) and limited selectivity (broad-range coverage) is desired.

Detector Operation

UV LampA photoIonization device contains of a vacuum lamp that emits UV light at a specific energy .Some common lamps avaible are 9.8eV, 10.6eV and 11.7eV.

Detector Operation

UV Lamp

- The UV light is generated by the excitation of the gas contained

- within the bulb (Krypton and argon are two gases commonly used).

- The gas in the lamp is excited with an electrical field or a radio frequency field.

PID Lamps

• The VX500 has a 10.6 eV lamp• A 11.7 lamp has a short life and needs special

treatment as dehydrating and frequent calibration, it is basically only suited for leak detection

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Gas In through filter UV Lamp

+ Electrode- Electrode

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Gas Out(No Longer Ionized)


10.6 eV

-In addition to the lamp the PID contains two electrodes a positive and a negative electrode :- The negative electrode is often referred to as the collecting electrode- The positive electrode is referred to as the biased electrode- The distance between the two electrodes is 20 000 of an inch.

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10.6 eV

- Gas molecules that pass through the light emitted from the ignited lamp are ionized if their ionization potential is less than the ionization potential of the lamp.

Detector Operation

UV Lamp

If the molecule’s ionization potential is above that of lamp, then nothing happens !

Detector Operation

UV Lamp

If the molecule’s ionization potential is less that of lamp,

then the molecule is ionized !

Detector Operation

UV Lamp-+

When a molecule is ionized an electron is removed forming a positively charged ion and an electron.

Principle of Operation

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The charged particules then move to the oppositely charge electrode.

Detector Operation

positive electrode

current

-

+negative electrode

The positive and negative ions are collected onElectrodes which produce a signal.This signal is directly proportional to the amont of ions present at the electrodes!

PID Principle of Operation

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Gas InUV Lamp


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Amplifier

100 PPM

Display

The signal is then displayed in parts per million (ppm) on theInstrument display.

PID Principle of Operation

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Display

As the ions leave the chamber they recombine with an electron andThe molecules exit in the same state as they entered !

PID sensors

SPECIFICATIONS

PID LampsLamp

Energy Gas Fill Window

Material Window

Characteristics Expected

Life )hours of operation(

10.6 eV Krypton Magnesium

Fluoride )MgF2( Hydrophillic window material, degraded transmittance with

continued exposure to moisture.

6,000 hours typical

11.7 eV Argon Lithium Fluoride )LiF(

Window material slightly soluble in water, seriously

degraded in presence of UV light

40 to 80 hours typical

Maximum 150

What does a PID detect?

• Volatile: readily vaporizable at a relatively low temperature.

• Organic: of, relating to, or containing carbon compounds.

• Compound: something formed by a union of elements.

VOC’s or Volatile Organic CompoundsVOC’s or Volatile Organic Compounds

As a rule of thumb organicAs a rule of thumb organic

solvents are VOC’ssolvents are VOC’s

Volatile Organic Compounds

• More accurate description: A VOC is Any hydrocarbon, except methane and ethane, with a vapor pressure equal to or greater than 0.1 mm Hg

Alkanes Alkenes Aromatics Alkynes Terpenes

ExamplesButane

(a paraffin)

ExamplesEthylene(Ethene)

ExamplesToluene

ExamplesAcetylene

(welding gas)(Ethyne)

Examples1Cineole(Eucalyptus

Oil)

ReactivitySlow

ReactivityFast

ReactivityMedium

ReactivitySlow

ReactivityFast

SourcesLiquid Fuel

ExhaustSolvents

Natural GasLPG

SourcesExhaustChemical

Feedstock

SourcesLiquid FuelSolvents

SourcesExhaustBiomass burning

SourcesNatural

Vegetation

Sensitivity and accuracy of a PID

• PID is capable of sub-ppm level detection of most volatile organic compounds (VOCs) (typical resolution 0.1 ppm)

• PID output per unit concentration ie. mV/ppm• A PID has the sensitivity but not the accuracy

Ionization Potentials and the Lack of PID Selectivity

Chemical Name IP )eV( Detected with a 10.6 eV lamp

Detected with a 11.7 eV lamp

Benzene 9.25 YES YES Toluene 8.82 YES YES m-Xylene 8.56 YES YES Ethylbenzene 8.77 YES YES Ammonia 10.20 YES YES Methylene Chloride 11.32 NO YES

Carbon monoxide 14.01 NO NO

Oxygen 12.08 NO NO Water 12.60 NO NO

Selectivity

• PID’s are not selective : Any molecule with an IP less than the IP of the lamp will be ionized.

• There is a need to consider:– What VOC’s am I likely to see?– What of these has the lowest acceptable level?– Calculate with response factors

Troublesome Conditions

• Presence of water vapor in sample stream causes quenching of the detector signal due to UV absorption and can short out the two electrodes

• Oxygen and methane are also UV absorbers. Significant changes in their concentration can cause both gain and background changes in the PID signal

Effect of Environmental Conditions on PID Signal

• Variation in pressure and temperature will have an effect on PID response. These effects will be compensated by the instrument.

• For maximum accuracy: Calibrate instrument in environmental conditions as close to sample conditions as possible

PID Lamps Require Periodic Cleaning

• Dust, dirt, or oil residue on lamp window will degrade the the performance of the PID.

• The frequency of cleaning will depend on the application. As a rule of thumb, under normal conditions the lamp should be cleaned after every 40 hours of service.

1 - Methanol1 - MethanolSolvent cleaning with methanol, will save time and may be sufficient depending on the type and amount of residue on the lamp window. Use a q-tip and gently clean lamp window.

Method of CleaningMethod of Cleaning

Method of Cleaning

2 - Abrasive Abrasive cleaning or Polishing “cuts” away a

very thin layer of lamp widow and will restore the lamp window to like new condition.

After cleaning, the lamp requires a burn-in period until the output of the lamp stabilizes.

- Lamp burn-in is 24 hrs.-

Photo, or the “light source”

• Handle the lamps by grasping their bodies.

• Never touch the lens. Touching the lens transfers oil which will decrease the UV output.

Troublesome Compounds

• Compounds that have a tendency to condense on the inner surfaces of the detector can cause signal drift.

• Ethylene behaves erratically• Ammonia causes severe degradation of

detector performance

PID Applications• Petrochemical• Oil and Gas• Hazmat• Aviation• Fire Departments• Environmental• Drug Enforcement

DETECTOR TUBES

• Measure of low concentrations• specificity to one gas• easy to use.• Low cost• is often the complement of the standard gas

detection systems.

Dust particules detection :principles

• Backscattering:LASER light backscattered by dust particules (analyser)

• POSTDIFFUSION: LASER light postdiffused by dust particules (analyser)

• in-situ measurement of smoke opacity• Particules detection by triboelectric effect (probes)

TECHNICAL

INFORMATIONS

Effects of Air Currents and Barriers

Number of detectors : Number of detectors :

• The number of detectors required for an application depends on a number of factors:

• plant layout, air flow pattern, type of gas to be monitored, degree of protection ...

ATMOSPHERICTESTING

TOP

MIDDLE

BOTTOM

Sample When / Where?prior to entry

top, middle & bottom continuously during entry**

prior to re-entry

Sample Why?stratification / weights / mix

Atmospheric Testing

-There may be no hazardous atmosphere within the space whenever any employee is inside the space

Atmospheric Testing

METHANE (lighter than air)

Atmospheric Testing

METHANE (lighter than air)CARBON MONOXIDE (slightly lighter than air)

Atmospheric Testing

METHANE (lighter than air)CARBON MONOXIDE (slightly lighter than air)

HYDROGEN SULFIDE (heavier than air)

Atmospheric Testing

-Before an employee enters the space, the internal atmosphere shall be tested for the following conditions in the order given:

Sample What? What Levels?

– Oxygen content 19.5 - 23.5%

– Combustible Gases 10% LEL

– Toxic Gases Depends on gas type

Testing recommendations for gas monitoring instrumentation.

• How often gas monitoring instruments be tested and calibrated ?

Testing recommendations for gas monitoring instrumentation

• Gas monitoring instrumentation should be treated like any other piece of lifesaving equipment.

• It should be tested and calibrated on a regular basis.

• The safest approach to testing gas monitors is to function test or calibrate them prior to each day’s use (mines …) !

When it comes to testing and calibrating gas monitoring equipment ?

• Things to consider :• Instrument use• Abuse experienced in the field• Gas exposures in fields ( high

levels )• Operature use ( shocks or

abuse …)


• A function test consists of exposing each sensor in the gas monitor to a known concentration of gas in excess of the lowest alarm set-point.

• The instrument should respond to the gas concentration by going into alarm

• If the sensors do not respond to the applied gas: the instrument will be calibrated …

• A calibration has become a very simple, sometimes automated, process

• A calibration consists of exposing the instrument sensors to a known concentration of gas, making appropriate response adjustments to ensure the instrument it reading accurately :

• zero setting in a pure air and span setting with a known concentration of gas.


• recommend a regular test according to the using :before each day’s usage sensitivity must be tested on a known concentration of gas

• and a minimum interval of calibration every 6 months ( industries) or every year (domestic market) .

Gas tester

Engineering

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