Transcript
Air Monitoring
Why Monitor the Air? OSHA Requirements: Air monitoring shall be used to identify and quantify airborne levels of hazardous substances and safety and health hazards in order to determine the appropriate level of employee protection needed on site. 1910.120(h)(1)(ii) Dangerous gases present? What gases may be present? Identify if dangerous levels of a gas are present.
Air Monitoring Devices Combustible Gas Indicator (CGI) Oxygen Meter Photoionization Detector Flame Ionization Detector (FID) Radiation Monitors Single Gas Meters Colorimetric Tubes
Combustible Gas Indicator (CGI) Measures the presence of a variety of combustible gases/vapors for confined space work sites where explosive and combustible gases are a potential danger.
Lower Explosive Level (%LEL) Measuring lower explosive limit: 0% to <10% LEL – continue to monitor levels and continue to work Action Level >10% LEL back out and re-assess the situation • Gasworks • Oil rigs • Chemical plants • Refineries • Environmental applications • Welding projects • Sewer engineering
Combustible Gas Indicator (CGI) Personal 4-Gas Monitor • Lower Explosive Limit (LEL) of a variety of combustible gases • Oxygen (O2) • Hydrogen Sulfide (H2S) • Carbon Monoxide (CO)
Why Monitor for Oxygen? Atmospheric Oxygen Content = 20.9% Acceptable ambient air breathing range = 19.5% - 23.5% Anything above or below that range – assess the situation and respond properly • >21% oxygen enriched (combustion could be a danger) • >19.5% minimum for safe entry • 16% impaired judgment and breathing • 14% faulty judgment and rapid fatigue • 6% difficulty breathing with death imminent in minutes
Why Monitor for Hydrogen Sulfide? Respiratory failure after prolonged exposure • H2S will deaden your sense of smell. Toxic • H2S mixes with the water in our lungs forming a weak acid. (Pulmonary Edema) SCBA or Supplied Airline Respirator are the two types of respiratory protection acceptable (only to be used if engineering controls are not feasible to control exposure to H2S gas)
Why Monitor for Hydrogen Sulfide? Flammable • Explosive limits - LEL 4.3% & UEL 46% • H2S fires produce a toxic gas: sulfur dioxide (SO2) is the main byproduct of a H2S fire. Flammability Range Over 44% = Too Rich to Burn UEL H2S = 44% or 440,000 ppm LEL H2S = 4.0% or 40,000 ppm Below 4.0% = Too Lean to Burn
Hydrogen Sulfide Exposure Limits • • • • • •
IDLH = 100ppm OSHA PEL for H2S is 20ppm ceiling concentration OSHA Peak exposure limit of 50ppm for no more than 10 minutes (if no other measurable exposure occurs) NIOSH REL for H2S is 10ppm ceiling ACGIH TLV-TWA for H2S is 1ppm ACGIH TLV-STEL for H2S is 5ppm Inhalation of 500-1000ppm will cause rapid unconsciousness and death
Hydrogen Sulfide (H2S) Other properties: • Corrosive • Invisible • Water and Oil Soluble • Can exist as liquid at low temp and high pressure • Heavier than Air (will settle in depressions) • Odor of Rotten Eggs (at low concentrations) • Sweet smell/taste (at higher concentrations)
Where is Hydrogen Sulfide? Naturally in crude production, natural gas, volcanic gases, hot springs Decomposition product from human and animal wastes: sewage treatment facilities, sediments of fish aquaculture, and manure Industrial sources: refineries, natural gas plants, petrochemical plants, coke oven plants, kraft paper mills, food processing plants, tanneries Human sources: bacteria in mouth and gastrointestinal tract Confined Spaces, Reservoirs, Dams
Why Monitor for Carbon Monoxide? Colorless, Odorless Gas – detection is the only was to know if this dangerous gas is present.
Where is Carbon Monoxide? Found in combustion fumes produced by cars, trucks, small gasoline engines, lanterns, burning charcoal and wood, gas ranges and heating systems. CO from these sources can build up in enclosed or semi-enclosed spaces. People and animals in these spaces can be poisoned by breathing it.
Carbon Monoxide Exposure Limits •
• •
•
IDLH = 1200ppm OSHA PEL-TWA for CO is 50ppm NIOSH REL-TWA for CO is 35ppm NIOSH REL for CO is 200ppm ceiling ACGIH TLV-TWA for CO is 25ppm
Photoionization Detectors (PID) Measure volatile organic compounds and other gases in concentrations from sub parts per billion to 10,000 ppm. A PID may produce instantaneous readings and operate continuously. PIDs are used as monitoring solutions for: • Lower explosive limit measurements • Ammonia detection • Hazardous materials handling • Arson investigation • Industrial hygiene and safety • Indoor air quality • Environmental contamination and remediation • Cleanroom facility maintenance
Flame Ionization Detector (FID) TVA-1000 PID/FID Combination Multi-Gas Monitor – PID function and 4 other gases
Radiation Monitors Geiger-Mueller Pancake Probe • Uses ionization to generate electric current • Detection of Alpha, Beta, and Gamma – Sensor must be near alpha source to be effective
• Used for contamination surveys – Large surface areas – Geiger-Mueller Pancake Probe
Radiation Alert-Monitor 4 • Alpha, Beta, Gamma, X-ray
Single Gas Meters Measures specific, single contaminants in ppm. Some calculate PEL and STEL with data loggers. Limitations: • Cross sensitivity • Sensor life affected by age and concentrations • Humidity reduces accuracy • Needs routine sensor calibration and replacement • Limited number available : CO, H2S, Ammonia (NH3), Chlorine Gas (CL2)
Colorimetric Indicator Tubes Detector tubes safely allow users to perform field screening and tests for the presence of hazardous and toxic gases, and vapors at a very low cost-per-sample. Detector tubes are easy to use and provide a low-cost method of routine or spot sampling for gases and vapors. The system is perfect when sampling for a known target gas.
Colorimetric Indicator Tubes Detector tubes indicate amount of gas by color change of chemically coated granules in a glass tube. • Rae Pump • Sensidyne Pump • Drager Pump
When to Monitor the Air 29 CFR 1910.120(h) Upon initial entry (investigation), representative air monitoring shall be conducted to identify • Any IDLH condition • Exposure over PELs or other published exposure levels • Other dangerous condition such as the presence of flammable atmospheres or oxygen deficient environments Periodic Monitoring • Shall be conducted when the possibility of an IDLH condition or flammable atmosphere has developed or when there is indication that exposures may have risen since prior monitoring.
Other Monitoring Reasons When work begins on a different portion of the site. When contaminants other than those previously identified are being handled. When a different type of operation is initiated (e.g., drum opening as opposed to exploratory well drilling). When employees are handling leaking drums or containers or working in areas with obvious liquid contamination (e.g., a spill or lagoon).
Air Monitoring Selection Considerations Purpose Sensitivity Intrinsic Safety Portability
Remember No one instrument does it all Instruments require TLC and upkeep Must recognize inherent limitations Read the manual! Breathing zone readings are important, also sweep high and low Keep instruments warm in cold weather to prolong run time Know your action levels and what the alarm levels are set at on your instrument!
