Gas equipment is installed on a roof 4 feet from the edge of the roof, how high must the railing be?

The height of the railing installed around gas equipment on a roof is determined by safety regulations to prevent falls and ensure worker safety. In Florida, the general requirement for guardrails is 42 inches in height when working at elevations where there is a risk of falling.

Since the question specifies that the gas equipment is placed on the roof at a height that can pose a risk to workers, maintaining a railing height of 42 inches ensures compliance with safety standards. This height provides adequate protection against potential falls, which is especially important when working near the edge of a roof.

While the other options might seem valid, they do not meet the safety code requirements for protecting against falls from elevated surfaces. Thus, the choice of 42 inches reflects the proper regulation that must be followed for such installations.