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Posted By Jeremy R. Manderson
Peter,
Input from Canadian and American HSE Industry. I have been in this business for many years. I have cut and pasted some data, including my personal input.I trust you will find this of interest. Post a note if you need further direction, I will arrange to send you some instruction data.
Selecting or using a gas detector should be based on the hazard faced. Unfortunately far too many user/purchasers make one of the largest and most crucial single equipment expenditures without really understanding what they are buying or using.
Sensors and their capabilities are the single most important factor when choosing a gas detector, yet more often than not, decisions are based on size, price, bells and whistles and other such features that have nothing to do with the instrument’s detecting abilities.
There are two categories of gas detection instruments: indirect reading and direct reading. With indirect reading instruments, samples must be sent to the laboratory for analysis: direct reading instruments provide their information at the time of sampling. Since the primary objective of gas detection in confined space operations is to immediately warn the entry team of adverse atmospheric changes, direct reading instruments are the only safe source of sampling information. There are a number of direct reading portable gas detectors on the market today.
Gas detectors come in a variety of sizes, shapes, colours and sensor configurations. For confined space work, it is necessary to monitor for oxygen deficiency/enrichment, combustible gases and toxics. Therefore an instrument capable of dealing with these three issues is necessary.
Gas detection manufacturers produce instruments with a variety of sensor configurations. One should be fully aware of the different sensor types and the capabilities. Just because catalogues or advertisements say that their instrument covers these three main parameters doesn’t mean that it will provide entry teams with the required protection. Never assume that instruments will work for specific applications without applying two important criteria:
Confined Spaces Recognition Evaluation Control Compliance Training Other Confined Spaces Many workplaces contain spaces that are considered "confined" because their configurations hinder the activities of any employees who must e
http://www.osha-slc.gov/SLTC/confinedspaces
Check out all categories including gas testing equipment.
Links to confined space entry information on the web.
http://www.pp.okstate.edu/ehs/links/conspace.htm
Atmospheric Testing
Atmospheric test data is needed prior to entry into any confined space.
Atmospheric testing is required for two distinct purposes: evaluation of
the hazards of the permit space and verification that acceptable conditions
exist for entry into that space. If a person must go into the space to
obtain the needed data, then Standard Confined Space Entry Procedures
should be followed (i.e., rescue team, attendant, entry supervisor).
Before entry into a confined space, a qualified person should conduct
testing for hazardous atmospheres. The internal atmosphere should be
tested with a calibrated, direct-reading instrument for the following, in
the order given:
* Oxygen content,
* Flammable gases and vapors, and
* Potential toxic air contaminants.
Testing equipment used in specialty areas should be listed or approved for
use in such areas. This listing or approval should be from nationally
recognized testing laboratories such as Underwriters Laboratories or
Factory Mutual Systems. Check out U.K. requirements
Evaluation Testing
The atmosphere of a confined space should be analyzed using equipment of
sufficient sensitivity and specificity The analysis should identify and
evaluate any hazardous atmospheres that may exist or arise, so that
appropriate permit entry procedures can be developed and acceptable entry
conditions stipulated for that space. Evaluation and interpretation of
these data and development of the entry procedure should be done by, or
reviewed by, a technically qualified professional (e.g., OSHA consultation
service, certified industrial hygienist, registered safety engineer,
certified safety professional).
Verification Testing
A confined space, which may contain a hazardous atmosphere, should be tested
for residues of all identified or suspected contaminants. The evaluation
testing should permit specified equipment to determine that residual
concentrations at the time of testing and entry are within acceptable
limits. Results of testing (i.e., actual concentration) should be recorded
on the permit. The atmosphere should be periodically retested to verify
that atmospheric conditions remain within acceptable entry parameters.
Initial testing of atmospheric conditions and subsequent tests after a job
has been stopped should be done with the ventilation systems shut down. If
the confined space is vacated for any period of time, the atmosphere of the
confined space should be retested before re-entry is permitted. Further
testing should be conducted with ventilation systems turned on to ensure
the contaminants are removed and that the ventilation system is not causing
a hazardous condition.
13.9.3. Acceptable Limits
The atmosphere of the confined spaces should be considered within
acceptable limits whenever the following conditions are maintained:
* Oxygen - 19.5% to 23.5%,
* Flammability - less than 10% of the Lower Flammable Limit (LFL), and
* Toxicity - less than recognized ACGIH exposure limits or other
published exposure levels (e.g. OSHA PELs, NIOSH RELs).
Whenever testing of the atmosphere indicates levels of oxygen,
flammability, or toxicity that are not within acceptable limits, entry
should be prohibited until appropriate controls are implemented. If the
source of the contaminant cannot be determined, precautions should be
adequate to deal with the worst possible condition in the confined space.
If there is the possibility that the confined space atmosphere can become
unacceptable while the work is in progress, the atmosphere should be
constantly monitored and procedures and equipment should be provided to
allow the employees to quickly and safely exit the confined space.
Jeremy R Manderson
HSEQ Management Specialist
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