(2) Example 2. Workers are engaged in a process that results in the
production of ozone (03). Throughout most of the 8-hour shift, the process, the
concentration reaches 0.005-ppm. However, at four steps in the process, the
concentration reaches 0.5-ppm, for about l2 minutes each time. These four instances of
0.5-ppm concentrations are 90 minutes apart.
(a) Refer to preceding paragraphs and to Appendix E; then answer
1 What is the TLV for ozone?
What is the STEL for ozone?
3 Do the concentrations to which these workers are periodically
exposed exceed standards (that is, are they unacceptable)?
1 By referring to Appendix E, we determine that the TLV for ozone
is 0.l ppm as a ceiling value.
2 There is no STEL for ozone.
3 Remember, the ceiling value is a maximum concentration to
which workers may not be exposed for any time period.
4 Because the actual concentration exceeds the ceiling limit, this
situation does not meet standards, that is, it is unacceptable; control measures to
reduce the concentrations, or to protect the workers from the excessively high
concentration, will be necessary.
(3) Example 3. A soldier working in a laboratory uses formaldehyde
routinely. The exposure in his breathing zone usually is for 20 minutes. The soldier
believes that he is in no danger from these short periods of 2-ppm concentration.
(a) Is he correct, or should some action be taken to control the
(b) Solution: From Appendix E, we determine that although the TLV for
formaldehyde is 1.0-ppm, this substance has been assigned a STEL which means that
the STEL region must not be exceeded for longer than 15 minutes. This soldier's health
is in jeopardy and control measures are imperative.