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gas detectors (confined spaces and more) E.W. (Ev) Carefoot, P.Eng., CIH, CRSP Salus Services Limited
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BC Municipal OH&S Conference 2011 Vancouver, BC November 6-8, 2011
Presentation caveats….
• Presenter has NO affiliation with a gas detection or instrumentation manufacturer, supplier, distributor, rental organization…
• Where a particular manufacturer’s equipment is illustrated, this does not suggest or imply a preference for it, nor that it has any benefits above that of any other manufacturer.
• If a particular manufacturer’s equipment is not illustrated it is not because of choice to not show their products. If I missed your product it is an oversight. B
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Gas Detectors
• Why do we need them?
• What can we choose from?
• How do they work?
• How do we maintain them?
• Where, when, and how do we use them?
• What do they tell us?
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Why do we need them?
Canaries only provide so much warning…
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The purpose of gas detectors/monitors is… 1. To detect the gas or vapor being monitored, and 2. To provide a warning or alarm.
Some portable equipment we can also use to investigate and assess worker exposures for comparison to exposure limits.
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What can we choose from…
• Electronic instrumentation
• Other direct reading sampling methods
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Equipment Selection
• Accuracy • Environmental operating
range: • Remote sampling
capability • Operating temperature • Relative humidity
• Intrinsic safety for explosive atmospheres
• Specificity for contaminant of interest
• Warm-up time • Response time
• Ruggedness • Ease of use and
maintenance • Pump configurations • Sensor and battery life • Data-logging capabilities • Software • Vendor support
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“Simplicity, reliability, & low maintenance”
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How do they work?
• Sensors
• Electrochemical (EC)
• Catalytic combustion (“bead” / Pellistor)
• Infrared (IR)
• Photo-ionization detector (PID)
• Transmitter
• Control Module
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Gas sensors…
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VOCs detected by PID… Cumene Cyclohexane Cyclohexanone Decane Diethylamine Dimethoxymethane Ethyleneglycol Ethylacetate Ethylene Heptane Hexane Iso-amylacetate Iso-propylamine Iso-propylether Iso-butanol Iso-butylene Iso-octane Iso-phorone
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n,n-Dimethylacetoamide 4-Hydroxy-4-methyl-2-pentanone Acetone Acetophenone Amylacetate Benzene Bromomethane Butadiene Butylacetate Tetrachloroethylene Trichloroethylene Dichloroethane Ethylbenzene Ethylacetoacetate Chlorobenzene
Meta-xylene Mesityloxide Methyl Isobutyl Ketone Methyltertiarybutylether Ortho-xylene Octane Para-xylene Phosphine Propylene Propylene Oxide Pyridine Quinoline Tertiarybutylamine Trisdichloroethene Tetrahydrofuran Thiophene Toluene
1,4-Dioxane 1-Butanol 1-Propanol 1,2,3-Trimethylbenzene 1,2,4-Trimethylbenzene 1,2-Dibromoethane 1,2-Dichlorobenzene 1,3,5-Trimethylbenzene 1-Methoxy-2-propanol Methylacetate Methylacrylate Methylacetoacetate Methylbenzoate Methylmethacrylate 2-Butanone 2-Pentianone 2-Propanol 2-Methoxyethanol
How do they work? Configurations – K I S S …
• Screen Selection
• Confidence beep
• Alarm Settings
• Datalogging
• User / site
• Date/time/temperature
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How do they work?
Alarm Settings • What is the purpose of an
alarm? • What alarms are found on gas
detection equipment? • Equipment failure or operation
warning • Multi-staged alarms (1/2/3 stage) • Time-weighted average (TWA) • Short term exposure limit (STEL)
• Audible, lighted, or vibration • Latching or NON-Latching
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Alarm notifications…
• LOW battery
• Battery fail
• OR / OL (over range / over limit)
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Alarm settings
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AGENCY Carbon Monoxide (CO) Oxygen (O2)
LOW HIGH TWA STEL LOW HIGH
WorkSafeBC 2009* 13 25 25 100 20.5 -
Manufacturer 1 35 70 35 400 19.5 23.5
Manufacturer 2 25 50 25 400 19.5 23.5
Manufacturer 3 35 50 35 200 19.5 23.5
Manufacturer 4 25 100 25 100 19.5 23
Manufacturer 5 35 100 35 100 19.5 23.5
Examples of manufacturer default alarm settings
*WorkSafe BC Bulletin WS 2009-03 Incorrect use of monitoring equipment in confined spaces can endanger workers
Alarm settings
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WorkSafeBC Bulletin WS 2009-03 Incorrect use of monitoring equipment in confined spaces can endanger workers
How do they work? Screen choices
• “Cal due” OR “Last Cal”
• Read screen
• Peak
• TWA (time-weighted average)
• STEL - short-term/15 minute
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Datalogging
• Logging intervals (1sec, 30sec, 1min, 5min, 15 min)
• Log on alarm
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How do we maintain them? FIXED GAS
• Regular calibration
• Monthly bump test • Manual
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8.0 CALIBRATION OF SENSOR / TRANSMITTERS Frequency: All sensors require regular calibration maintenance to ensure accuracy and indeed to confirm that they have not expired. Electrochemical sensors installed in applications such as parking facilities should be gas calibrated a minimum of once per year. A frequency of once every six months is preferred. Sensors installed in applications that must specially meet the need for Occupational Health & Safety standards should be gas calibrated once every six months. These sensors should be gas tested once per month with a known concentration of target gas.
How do we maintain them? PORTABLE GAS
1. Regular calibration
• Manual
• Automatic
2. Functional (Bump) testing
3. Fresh air setup or “Zero” adjustment
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Calibration, bump…what’s what?
Full Calibration
The adjustment of an instrument’s response to match a desired value compared to a known concentration of test gas.
Function (Bump) Test
A means of verifying calibration by using a known concentration of test gas to demonstrate that an instrument’s response to the test gas is within acceptable limits.
Sensor Challenge
Exposing a monitor's sensor(s) to a concentration of calibration gas, which will cause the monitor's alarms to function.
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ISEA Statement on Verification of Calibration for Direct Reading Portable Gas Monitors Used in Confined Spaces 11-20-02
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Fresh air (zero) adjustment
Fresh Air Setup / Zero Adjustment
Adjustment of sensors prior to calibration, bump test, or in field to set sensors to 20.9% (21%) oxygen and 0 ppm toxic sensors
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Maintenance
Condition of:
• Sensors (poisoned)
• Pump
• Battery
• Remote sample probes
• Dust and hydrophobic filters
Sensor replacement
• Oxygen 2Pb + O2 → 2PbO
• CO/H2S non-consumptive
• LEL different than others
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Where and when are they used FIXED SYSTEMS
• Arenas • Ammonia • Carbon monoxide • Nitrogen dioxide
• Pools • Chlorine • Ozone
• Landfill site • Methane
• Greenhouse • Carbon dioxide
• Parkade • Carbon monoxide • Propane
PORTABLE EQUIPMENT
• Area (e.g. confined space) • Pre-entry, AND
• Continuous or intermittent
• Work task monitoring • TWA – time-weighted average
• STEL – 15-min average
• Exposure assessment
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How we use them…
PORTABLE GAS
• Pre-use Routines
• Battery
• Functional (bump) testing
• Peak – clear
• Fresh air setup – “zero”
• Sampling practices
• Diffusion or remote
• Instrumentation position / stratification
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Must have an understanding of:
• Material to be sampled
• Density
• Solubility
• Clear understanding of equipment limitations
• Area and expected atmospheres
• Responses when alarms activated
How we use them…
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How we use them…
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What do they tell us? “Current conditions” • What are acceptable atmospheric conditions?
• Confined Spaces Entry Hazardous Atmospheres
• OHSR Part 9 - LOW , MODERATE, HIGH
• “Clean Respirable Air” • Approximately 20.9% oxygen
• No flammable gases
• No toxic contaminant exceeding 10% of an exposure limit
• Immediately Dangerous to Life or Health (IDLH)
• Exposure Limits (ELs) and Threshold Limit Values (TLVs)
• Time-Weighted Average (TWA – 8 hour or adjusted)
• Short term (15-min STEL)
• Ceiling Limits
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CH4 & low hazard atmospheres
• Methane - CH4 - a common flammable gas, also has an TWA exposure limit of 1,000 ppm (C1 to C4 hydrocarbons)
• Flammable or LEL sensors read in a % of the lower explosive limit or LEL or %LEL (which is different than %air)
• Methane explosive range of 5%air (LEL) to 15%air (UEL)
• 1%air = 10,000 ppm
• Methane LEL is 50,000 ppm so 1%LEL is 500 ppm
• LOW hazard atmosphere must not exceed 10% of a contaminants exposure limit: Methane = 100 ppm
• Resolution of LEL sensors is typically 1%LEL
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Response times
Response Time (t90):
The time for a sensor to reach 90% of its final stable reading. Typically an exposure of twice the t90 time is required to get a stable reading.
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Alarm conditions
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Past conditions…
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MChart 1 Carbon Dioxide Concentrations
Week 1: July 26 to August 2, 2000
CO2
“False” information
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10
0 P
PM
TES
T G
AS
SENSOR READING
LEL sensor correction
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LEL sensor correction
Training experience
• 4 gas detector kits
• Bump tested • 2 read “33%LEL”
• 2 read “81%LEL”
What happened?
• 2 kits were propane and 2 kits were methane
• Bump test gas reversed
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What don’t they tell us…
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• Appropriate sensor for gas/condition to be detected has to be present
• Oxygen sensor is not a “catch all”!
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Recordkeeping • Calibrations
• Function (bump) tests
• Datalogging
• Alarms
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Education and training
• Qualified Person • Training curriculum
• Selection • Equipment operation • Equipment Limitations • Configuration • Gas hazards and characteristics • Sampling and testing practices • Inspection and maintenance • Datalogging and interfaces • Data interpretation
• What’s available • Equipment Manuals • Quick Use Guides • CD/DVD/online training
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Summing up
• We need gas detectors to: 1. Detect the gas or vapor being monitored 2. Provide a warning or alarm
• Lots of selection
• Very specific in their operation
• Care and attention in their maintenance 1. Regular calibration 2. Functional (bump) testing
• Fixed and portable applications
• Education and training IS required
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Parting comments…
“When it comes to gas detection training, what you don’t know CAN hurt you!”
Dave Kuiawa, Director of Training Industrial Scientific Corporation 8
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“First to fall over when the atmosphere is less than perfect Your sensibilities are shaken by the slightest defect You live your life like a canary in a coalmine You get so dizzy even walking in a straight line…”
“Canary in a Coal Mine” excerpt The Police (1980)
Questions?
Thank you.
For more information please contact:
Ev Carefoot [email protected]
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