Sampling in Remote and Difficult to Reach Areas with Detector Tubes
From time to time the industrial hygienist or safety professional is tasked with monitoring for air contaminants in a remote location, such as with tank entry or other confined space entry. In those situations the standard four contaminant measurements are required (carbon monoxide, hydrogen sulfide, oxygen deficiency and combustibles) along with additional measurements for any other known contaminants not covered by those four tests. For example, in a refinery, worker entry into a gasoline storage tank would require the four standard tests and a test for the level of benzene, which is known to be potentially present as a component of gasoline. The electrochemical toxic gas sensors used in confined space entry instruments will not respond to benzene. While a typical combustibles sensor would respond to benzene at some level, it will not respond at the TLV level. A further test for benzene at the TLV level is required.
In such situations, a detector tube can often be utilized to detect the target gas at the TLV level. Indeed, detector tubes are available to conduct the benzene monitoring described above. The question then becomes, how can I sample remotely with a detector tube? Many versions of four-gas monitors are available in today’s marketplace for the monitoring of the four standard confined space tests, and those monitors offer accessories for conducting remote sampling for the safety of the operator. Detector tube systems also offer accessories to allow remote sampling, and such accessories are vital to the safety of the operator.
Storage tanks are often designed for top side entry, and it is common for the sampling to be conducted from the top of the tank or vessel. In those cases a flexible extension hose can be used to obtain the downward remote sample. Special extension hoses are available for our Sensidyne/Kitagawa hand pumps that connect to the front of the pump and position the detector tube at the opposite end of the hose. In this manner the tube itself is dropped into the tank, and there is no purge of the hose required. The field leak check is still done by placing an unbroken tube in the holder, locking the pump handle, waiting one minute, releasing the handle and observing any pump handle travel.
Flexible extension hoses are available from Sensidyne in two lengths, five meters (about 16 feet) and ten meters (about 32 feet). The limit to the length of such an extension hose lies in the internal volume of the hose. The hand pump must evacuate the area inside the pump and also inside the extension hose in order to initiate the air flow through the detector tube. The longer the extension hose, the lower will be the initial vacuum level, and the slower will be the air flow rate through the detector tube. For that reason, we limit the length to ten meters so as to keep the flow rate within a tolerance that will maintain the system accuracy.
In some cases a vessel must be sampled that does not allow topside entry. Examples might include a rotary kiln, a silo or bag house dust collector. In those cases a rigid extension would be desirable in order to sample remotely in any direction including straight up, diagonally or laterally. To accommodate such requirements Sensidyne offers a telescoping extension probe that allows sampling in any direction up to about three meters or ten feet. Again, the tube is located at the far end of the extension probe so no purge is required, and the field leak check is run as normal using an unbroken tube.
Remote sampling is sometimes essential to keep an operator out of harm’s way. Detector tubes can be used remotely by incorporating the appropriate accessories. For further information on these products contact our Customer Support Team.