TOXIC GAS INDICATORS

The Navy uses several types of toxic gas indicators. Some can only test for one type of gas. Others can test for several types of toxic gases, but only one type of gas at a time. The following discussion is based on the equipment that is most likely to be on your ship. When you use equipment on your ship, refer to the manufacturer's technical manual that is issued with the equipment.

Figure 6-37.-Bacharach universal gas sampler.

Bacharach Universal Gas Sampler

The Bacharach universal gas sampler (fig. 6-37) is used to test for carbon monoxide, ^{hydrogen sulfide,} carbon dioxide, chlorine, sulphur dioxide, and nitrogen dioxide. A different indicator tube and scale is used with the basic unit to check for each type of gas.

The following procedures should be used to test for carbon monoxide. However, the procedures discussed are the same for each of the gases.

1. Ensure that the orifice assembly is installed and the knurled clamp nut is finger tight. Ensure that the stop nut is in the correct position and the correct tube and scale are installed for the type of gas for which you are testing.

2. Unfold the scale frame and scale from the bottom of the sampler and swing it forward until it locks in place.

3. Slide the metal tip breaker on the bottom of the sampler back to open the tube breaker hole. Insert the indicator tube tip in the exposed hole and break off the tips to open both ends of the tube. Then push the slide forward to close the tip breaker hole.

4. Slide either end of the opened indicator tube through the wire loop scale. Continue inserting the tube until the tube tip is snugly inside the rubber tube connector of the sampler.

5. Depress the push button down as far as it will go and hold it there for several seconds. Release the push button quickly and allow it to return to its original position. A red line on the push button will be visible when the button is in the upright position.

6. When the red line is completely visible, wait 30 seconds before you examine the indicator tube for a brownish stain in the yellow-colored gel. If a stain appears, carbon monoxide is present in the area being tested.

7. Move the scale from right to left until only unstained gel appears in the short scale slot (A) to the left of the scale's zero bar (B) and only stained gel appears in the long scale slot. See figure 6-38. The stained gel includes all yellow gel that is visibly darkened by the carbon monoxide. The unstained gel is that portion of the yellow gel which is totally unaffected by the carbon monoxide. Read the scale at the point (C) where the stained gel and the white guard gel meet. To ensure maximum accuracy, rotate the indicator tube approximately 90 degrees to four positions. Then average your readings. The indicator tube in figure 6-38 has a reading of 0.015% carbon monoxide on the 3-pump scale.

8. If no stain is visible after 1 pump stroke, repeat steps 4 through 6 for a total of 2, 3, or 7 pump strokes for a greater sensitivity. When making the additional pump strokes, be sure to use the correct portion of the scale when you measure the length of the stained gel.

Figure 6-38.-Bacharach universal gas sampler test for carbon monoxide. 6-25