(a)    Selection. The court may direct that jurors, in addition to the regular panel, be called and impanelled to sit as alternate jurors. Alternate jurors, in the order in which they are impanelled, shall replace jurors who, prior to the time the jury retires to consider its verdict, become unable or disqualified to perform their duties. Alternate jurors shall be drawn in the same manner, have the same qualifications, be subject to the same examination, take the same oath, and have the same functions, powers, facilities, and privileges as the principal jurors. Except as hereinafter provided regarding capital cases, an alternate juror who does not replace a principal juror shall be discharged at the same time the jury retires to consider its verdict.

(b)    Responsibilities. At the conclusion of the guilt or innocence phase of the trial, each alternate juror will be excused with instructions to remain in the courtroom. The jury will then retire to consider its verdict, and each alternate will be excused with appropriate instructions that the alternate juror may have to return for an additional hearing should the defendant be convicted of a capital offense.