TITLE:

ES&H Manual

 

DOCUMENT ID:

Appendix 6160 Appendix T3

Atmospheric Testing of Confined Spaces

 

 

1.0            Introduction

 

Hazardous atmospheres in confined spaces are created most often when oxygen is depleted through oxidation (rusting and respiration, for example) or though organic material decay: “natural causes.”  Toxic, asphyxiating, and flammable gases or vapors at Jefferson Lab are usually introduced by man-made causes.  Examples:

 

·         carbon monoxide (CO) from nearby engines

·         inert (asphyxiating) gases such as nitrogen, helium, argon, and refrigerants

·         fuel gases from hot work; flammable solvents and cleaners

 

All PRCSs must be monitored for oxygen content and flammability.  In addition, when there is any potential for a toxic atmosphere, the concentration of the toxic substance is measured, using an appropriate instrument.  A selection of calibrated direct-reading instruments is maintained in the Safety Lab (Bldg.35) and may be checked-out to qualified Jefferson Lab staff.  Color-change (colorimetric) tubes and pumps are also available for specific substances.

 

Atmospheric testing is often performed by entry supervisors – staff who have completed Jefferson Lab’s confined space entry training, are able to assess the PRCS hazards and specify the controls needed for safe entry.  Testing may also be performed by monitors who have familiarized themselves with the instruments used for air testing in PRCSs.  As a minimum, the monitor must be qualified as an authorized entrant before making a confined space entry to take atmosphere readings.  The monitor, who may also be the attendant, is responsible to the entry supervisor while taking readings and keeps the entry supervisor informed of the results.

 

Text Box: Be aware that many documented confined space fatalities involved the use of chemicals that cause little or no acute effects in open air. Consider this example: A liter of xylene (a common solvent in high-performance industrial paints, adhesives, and coatings) evaporates inside an unventilated • 1000ft3 confined space. The resultant vapor concentration is over 7000 ppm. • Compare this to the recommended 8-hour exposure limit of 100 ppm. • Or to the Immediately Dangerous to Life or Health limit of 1000 ppm. At this concentration, xylene is an effective anesthetic, likely causing rapid loss of consciousness. It will also cause major damage to a number of body organs.

 

2.0            Air Monitoring Procedures

 

Step 1              Determine the type of atmospheric monitoring that will be needed; can processes taking place inside or near the PRCS generate air contaminants?  Can the air be tested at all depths prior to confined space entry?  Does the space have mechanical ventilation and is it operating?

 

If you are unfamiliar with the PRCS, review available information such as construction drawings (available at Facilities Management).  Check the history of the PRCS; i.e., prior work, previous permits and atmosphere readings.  Confer with cognizant ESH&Q staff if you are uncertain of the best approach.

 

Step 2              Obtain suitable air-monitoring instrumentation from the Jefferson Lab Safety Lab (Bldg. 35) or from your ESH&Q staff.  Ensure it has a current calibration date and has the necessary detection functions for the PRCS in question.  If needed, obtain accessory devices such as remote sampling pumps and extra lengths of tubing.  You may need a spare set of batteries if the instrument will be on continuously for several hours.  Request assistance from Safety Lab staff for proper use of instruments with which you are unfamiliar.

 

Text Box: NOTE: Testing is always mandatory for proper oxygen levels and for the presence of flammables. All of the direct-reading instruments available for loan from the Safety Lab have both of these functions. Some have toxic-detection capability as well. There are many possible toxic gases or vapors. Hydrogen sulfide and carbon monoxide are deadly, and their detection is a common additional feature on multi-function instruments. Other potential toxic or asphyxiating gases and vapors (CO2, helium, refrigerants, etc.) will likely be related to work being done within or closely adjacent to the PRCS. Monitoring should be application-specific; i.e., monitor for contaminants that are possible for the situation. Pay close attention to the work activity, location, materials in use and the atmospheric hazards they introduce.

 

Always request assistance from your division ESH&Q staff when you are uncertain about air-monitoring strategies.

 

Step 3              Meet with all personnel who will be involved with the confined space entry.  Assist in planning the PRCS confined space entry – including frequency of repeat monitoring.  Determine whether initial readings can be taken remotely; i.e., without entering the PRCS.

 

Step 4              Turn on the instrument in an open area (uncontaminated air), and allow it to perform its self-diagnostics.  Ensure there is ample reserve battery power.  Make certain that everyone who will use or rely on the instrument understands its display and audible alert(s).  All functions must operate normally.  If a detector cell fails, obtain another instrument.

 

Step 5              Perform or supervise initial air monitoring – ensuring that entrants have the opportunity to observe and ask questions.  Obtain a reading at representative depths, preferably by using extended tubing and auxiliary sampling pumps.  In order to assess “worst-case” conditions, it is best to test before ventilating or otherwise disturbing the air within the space.  Record the results – either on the Confined Space Entry Permit or on a log sheet.  Ensure entrants have the opportunity to witness the testing, and discuss the safety implications of the results with all those affected.

 

 

Remember: If you enter the PRCS to test the air, you must use the full entry precautions specified in ES&H Manual Chapter 6160 Appendix T4 General Procedure for Entry into Permit-Required Confined Spaces.

 

Text Box: NOTE: Significant oxygen enrichment or depletion may cause inaccurate combustible readings with some instruments.

 

Text Box: Most instruments in current production reliable readings for all hydrocarbon combustibles and mixtures, and you do not need to apply any correction factors to the displayed concentration. There are two important and dangerous exceptions: Acetylene and hydrogen levels are not measured accurately by many instruments. If these gases are suspected to be present, ensure the instrument is specifically rated for them or use colorimetric detector tubes.

 

Text Box: NOTE: Significant oxygen enrichment or depletion may cause inaccurate combustible readings with some instruments.

 

Text Box: NOTE: Carbon monoxide (CO) detector cells are especially prone to interference from other substances. They can even be temporarily “poisoned” by very high concentrations of some hydrocarbons. Most instruments have activated charcoal filter pads for the CO cell. These absorb hydrocarbons (HCs) and will help reduce this problem. Use a fresh, previously unopened pad if you will be sampling for CO and anticipate high HC levels.

 

Step 6              Determine a suitable strategy for repeat testing – how often, by whom, etc. – and what to do if the instrument alarms or indicates a trouble condition.

·         If the entrant is to carry the instrument into the space for continuous monitoring, ensure there are spare batteries on hand for the anticipated duration of the entry.  (A rule of thumb: most instruments will operate continuously no more than 5-6 hours without battery replacement.)

·         If there is to be a designated monitor (an attendant, for example), ensure he or she clearly understands the monitoring strategy.

·         Any time people are inside the PRCS and you detect an out-of-specification atmospheric condition, you must immediately warn the entrants and entry supervisor.

 

Text Box: NOTE: If you are using colorimetric indicator tubes, promptly write down the concentration as indicated by the length and degree of color change. The stained area will likely continue to change (+) after exposure, and the tube will become useless as a record. Be sure you read the tube instructions carefully for proper sample volume (pump strokes), interfering substances, and any temperature/humidity corrections that may be required. Also check the expiration date for the tubes; do not use them if the date has passed.

 

Step 7              When the entry is concluded, return the instrument to the Safety Lab.  If you noted any malfunctions or operational problems with it, inform the Safety Lab staff.

 

 

 

ISSUING AUTHORITY

APPENDIX AUTHOR

APPROVAL DATE

EFFECTIVE DATE

EXPIRATION DATE

REV.

 

 

 

ESH&Q Division

John Kelly

08/30/06

08/30/06

08/30/09

0

 

This document is controlled as an on line file.  It may be printed but the print copy is not a controlled document.  It is the user’s responsibility to ensure that the document is the same revision as the current on line file.  This copy was printed on 8/19/2009.