Maryland Labor and Employment Section 5-602
§ 5-602.
  (a)   (1)   In this section the following words have the meanings indicated.
    (2)   "Confined space" means a space that, by design:
      (i)   has limited openings for entry and exit; and
      (ii)   is subject to:
        1.   the accumulation of a combustible agent;
        2.   an accumulation of a toxic agent; or
        3.   a deficiency of oxygen.
    (3)   "Confined space" includes:
      (i)   a basin;
      (ii)   a bin;
      (iii)   a degreaser;
      (iv)   a duct;
      (v)   a pipeline;
      (vi)   a pit;
      (vii)   a sewer;
      (viii)   a silo;
      (ix)   a tank that is enclosed or has an open top;
      (x)   a tub;
      (xi)   a tunnel;
      (xii)   a vat;
      (xiii)   a process vessel; or
      (xiv)   a reaction vessel.
    (4)   "Maintenance work" means cleaning, inspection, maintenance, painting, repair, servicing, or other similar work.
  (b)   A person described in § 5-101(d)(2)(ii) or (iii) may not allow or cause an individual described in § 5-101(c)(2)(iii) or (iv) to do maintenance work in a confined space, unless the Commissioner:
    (1)   grants written authorization based on a satisfactory showing that work practices in effect will protect the health and safety of the individual; or
    (2)   in accordance with Subtitle 3 of this title, passes an order for a variance.
  (c)   (1)   This subsection applies only to an employer who is a subcontractor.
    (2)   Each subcontractor who, under an original contract or subcontract, is to do maintenance work in a confined space shall give the Commissioner:
      (i)   at the commencement of the maintenance work, oral notice of the maintenance work to be performed; and
      (ii)   within 24 hours after the oral notice, written notice of the maintenance work.