Table 1

Time of sample collection and study design

Sampling period†DesignNNon-welding dayWelding dayNon-welding days‡
The previous morningThe previous afternoonMorning (preshift)Afternoon (postshift)The next morningMorningAfternoon
2006Overnight3535 samples35 samples35 samples
January 2010–February 2010Overnight3030 samples30 samples30 samples
June 2010–July 2010Overnight3333 samples42 samples42 samples9 samples
January 2011–February 2011Two-way66 samples6 samples14 samples14 samples8 samples8 samples
June 2011Two-way1414 samples14 samples14 samples14 samples
June 2012Two-way1616 samples16 samples16 samples16 samples

  • 44 sets of samples were qualified for postexposure overnight design; 99 sets of samples were qualified for pre-exposure overnight design; 44 sets of samples were qualified for two-way factorial design.

  • †74 welders participated in the study. Some welders participated in multiple sampling periods. We collected 509 samples in total.

  • ‡Non-welding days is within ±7 days’ interval from the welding day; besides, a few participants had additional samples collected at baseline (12 samples).