Five-gas comes of age

PIDs and a range of electrochemical sensors have become commonplace as extra sensors in conventional 4-gas confined space entry meters to protect workers from exposure to a broad array of toxic organic and inorganic vapors. New wireless transmission systems have opened up a host of safer and faster detection capabilities, requiring less operator involvement and thus saving costs.

Interchangeability of gas detection tubes and hand pumps

Users of gas detection tubes occasionally seek the convenience of using a single hand pump with different brands of tubes, to avoid the need to carry more than one pump. Several professional organizations recommend against such interchange. However, these recommendations appear to be based on a single study of pump designs that mostly are no longer in use. The present study was undertaken to determine if current hand pumps are interchangeable. Both piston-type and bellows-type hand pumps were evaluated by comparing pump flow profiles and test gas measurements with a variety of tubes. The results demonstrate that three piston hand pumps in common use (Sensidyne/Gastec GV/100, RAE Systems LP-1200, and Matheson-Kitagawa 8104-400A) are fully interchangeable. Two bellows pumps (Draeger Accuro and MSA Kwik-Draw) also are interchangeable with each other. Mixing of bellows and piston systems is often possible, but there are enough exceptions to conclude that such practice should be discouraged because it can give inaccurate readings. It is recommended that technical standards be adopted, such as total volume and an initial pump vacuum or a pump flow curve, to assess hand pump interchangeability. When two manufacturers' pumps meet the same standard and routine leak tests are conducted, interchangeability is scientifically valid and poses no risk to the end user while offering greater convenience.

Effects of light and presence of fish on lure display and larval release behaviours in two species of freshwater mussels

We investigated how two sympatric species of freshwater mussels transmit their parasitic larvae to fish hosts. We found that Villosa nebulosa and V. vibex both display large mantle lures to attract potential host fish, but V. nebulosa displayed only at night and V. vibex displayed mostly by day. Display periods were similar in the laboratory and in the field. In two laboratory experiments, we found that the frequency of lure display in both mussel species was unrelated to the presence of fish or to the species of fish present. However, both species released more larvae in the presence of a suitable host fish (Micropterus spp.) and a nonhost species (Cyprinella camura) than in the absence of fish. In all treatments, females released low numbers of larvae on a daily basis throughout the experiment. We also observed several, irregularly occurring major release events in which numbers of larvae released were from one to three orders of magnitude larger than minor, daily releases. In V. nebulosa, major releases occurred with suitable and nonsuitable host species; in V. vibex major releases occurred mostly with suitable host species. In an additional laboratory experiment, we found that V. vibex released large numbers of larvae only when the host fish was able to make physical contact with the mussel. Few larvae were released when no fish were present or when host fish were present but physical access to the mussel was restricted. These results show that, in mussel species that display lures, physical interaction with a fish is necessary to stimulate large releases of larvae and suggest that interactions with a suitable host species stimulate larger and more frequent releases than with nonhosts. Copyright 2000 The Association for the Study of Animal Behaviour.