Atmospheric Hazards. Hazardous Atmosphere 3/29/2017. Oxygen deficiency and enrichment Flammable gases and vapors Toxic contaminants

Transcription

1 2017 Wisconsin Safety Council Safety & Health Conference, Presentation by Tim Gackle, OSHA Training Institute April 11, 2017 Atmospheric Hazards Oxygen deficiency and enrichment Flammable gases and vapors Toxic contaminants Hazardous Atmosphere Based on NIOSH and OSHA statistics, about 40% of fatalities in permitrequired confined spaces are due to atmospheric hazards Often invisible and odorless Much too often, no testing is conducted at all 1

2 Appendixes Appendix B Procedures for atmospheric testing Appendix E The broad range sensor is best suited for initial use where contaminants have not been identified They do not measure the levels of specific substances. Therefore, substance-specific devices, which measure the actual levels of specific substances, are best suited for use where actual and potential contaminants have been identified. Stratification Gases lighter than air tend to rise; gases heavier than air tend to sink The density of a gas is roughly equal to its molecular weight (molecular weigh of air 29 g/mol) Vapor density is the measure of vapor s weight compared to air (vapor density of air = 1.0) Stratification Examples of lighter than air gases and vapors Acetylene Ammonia Hydrogen cyanide Methane Examples of heavier than air gases and vapors Hydrogen sulfide Gasoline Solvents (MEK, toluene, etc.) 2

3 Direct-Reading Instrumentation Calibration by the manufacturer Intrinsically safe Batteries; charging Read the manual and follow it Decontamination Radiofrequency radiation Direct Reading Instrumentation Warm-up time Response time Sensitivity Specificity Interferences Environmental conditions Functional Bump Test Apply calibration gas of known concentration to sensors and observing the readings and alarm function Only provides verification of sensor performance NOT A CALIBRATION though you should record the results 3

4 Calibration Follow the manufacturer s manual Use the appropriate calibration gas & flow rate (regulator) Document Send to manufacturer at predetermined frequency Four Gas Meter Contains oxygen, explosibility (combustible) and carbon monoxide gas sensors Additional toxic sensor typically hydrogen sulfide Chlorine, ammonia, nitrogen dioxide, sulfur dioxide Oxygen Sensor Reading in percent oxygen Generally last one to two years Should be read first because other sensors may have oxygen dependency 4

5 Question #1 If the Oxygen reading on the four gas meter reads between 19.5% and 23.5%, is the Permit Required Confined Space safe to enter? Let s look at an example What if the reading was 20% Oxygen is that safe? 100 % AIR - 5 % GAS X 95 % AIR 95 % AIR x.21 % Oxygen % Oxygen ~ 20 % O 2 Concentration of Gases and Vapors = %Volume 1,000,000 = 100% 100,000 = 10% 10,000 = 1% SAFETY (%LEL) 1,000 = 0.1% HEALTH (PEL) 100 = 0.01% 10 = 0.001% 1 = % 5

6 So the real questions should be? What is? Is of dangerous? Answer #1 If the Oxygen reading on the four gas meter reads between 19.5% and 23.5%, is the Permit Required Confined Space safe to enter? Answer: Explosibility (Combustible Gas) Sensors 6

7 Explosibility (Combustible Gas) Sensors Give readings in percent of LEL of the calibrated gas Do not detect flammable liquids with flashpoints above 90 F Give erroneous readings in oxygen deficient and enriched spaces Question #2 If the Oxygen sensor reads 13%, and the LEL sensor (explosibility) reads 12%, what can we say about flammable vapors in this space? Answer #2 If the Oxygen sensor reads 13%, and the LEL sensor (explosibility) reads 12%, what can we say about flammable vapors in this space? Answer: 7

8 LEL Correlation Factors Industrial Scientific Corp.-Sensors & Manufactured After 3/93 Explosibility (Combustible Gas) Sensor Poisons Silicones Tetraethyl lead Halogenated hydrocarbons High concentrations of sulfides High concentrations of flammable gas High concentrations of oxygen Toxic Gas Sensor Gives reading in part per million () Interferences may be a problem Give erroneous readings Poison the sensor 8

9 Sensor Cross-Sensitivity Confined Space #1 #1 - (Paint Operation) A common paint solvent/drying accelerant is stored in a 250 gallon tank near an automotive spray finishing operation. The filter bank for the spray booth is accessible behind the booth through two small hatch openings, for filter replacement. The booth ventilation must be shut off and locked out to allow filter maintenance. Unknown to the filter maintenance worker, the solvent tank has been leaking and the solvent traveled into the filter bank (confined space). Due to olfactory fatigue, the worker has poor sense of smell for the solvent odor. The space requires air testing to ensure a safe atmosphere. Record the results of your monitoring. Bucket Test Number Levels % O 2 % LEL #1 T B CO H 2 S Additional Measurements Comments Confined Space #2 #2 - (Fuel supplier/pit) A storm sewer lift station sits near a property line adjacent to a commercial heating oil distribution center. In the lift station 10 feet down, an oily slick is noticeable on the surface of accumulated water, and a petroleum odor is evident. Determine entry acceptability. Bucket Number Test Levels % O 2 % LEL CO H 2 S Additional Measurements Comments T #2 B 9

10 Confined Space #3 #3 - Two volunteer fire fighters are called out to remove a dead animal from a well. To pump the ~12 feet of water out of the well before entering, a gasoline engine-powered pump was lowered down to a small ledge located inside the well. The engine was started, but the pump could not be primed. The fire fighters are getting ready to enter the well to prime the pump. Is entry allowable? Why or why not? Bucket Test Number Levels % O 2 % LEL CO H 2 S Additional Measurements Comments T #3 B Confined Space #4 # 4 - (Fertilizer Plant) At a fertilizer processing facility, one worker is required to enter a 5,000 gallon liquid fertilizer holding tank to clear a drain valve. The holding tank has been pumped empty with auxiliary pumps. A residue remains inside the tank surfaces. After testing the atmosphere, the worker prepares to enter the tank. Is it safe? Why or why not? Note: SDS for the liquid fertilizer indicates 20% urea and 30% ammonium nitrate content, with a slight ammonia odor. Bucket Test Number Levels % O 2 % LEL CO H 2 S Additional Measurements Comments #4 T B Photo-Ionization Detector (PID) Non-specific detection Used commonly for detection of hydrocarbons Reading is a ratio of response of the contaminant relative to the reference (calibration) gas used typically isobutylene Response compared to internal library or a table in the manufacturer s manual Adversely affected by age of lamp, cleanliness of lamp, humidity, etc. 10

11 Hand Pump & Detector Tubes Glass tubes give color response on introduction of specific gas or vapor More specificity Use tubes that match same manufacturer as pump Use tubes at same temperature as sampled environment Leak test the pump, record results Sampling error typically 25 35% Tubes have expiration date If a properly calibrated electronic fourgas instrument is used to evaluate the atmosphere in a permit space, are the sensor readings depicting the true concentration of the atmospheric hazards contained in the space? Have we Cleared the Air? Tim Gackle, Industrial Hygienist Safety & Health Instructor, OSHA Training Institute, Arlington Heights, IL Contact information: gackle.timothy@dol.gov Ph: Thank you WSC and attendees! 11