On roofs which is ____ feet or less in width, the use of a safety monitoring system alone is allowed.

The correct answer is based on industry safety standards that dictate when a safety monitoring system can be used alone without additional fall protection measures. Specifically, for roofs that are 50 feet or less in width, safety monitoring systems are considered adequate. This width allowance is grounded in the understanding that narrower areas may offer less risk of workers falling, thus permitting a monitoring system to effectively oversee and protect those working on the roof.

Those who may be familiar with workplace safety regulations understand that a safety monitoring system involves using a trained person to keep watch over workers and warn them of potential hazards. The allowance for this system to be used without supplemental measures in specific width conditions reflects a balance between safety requirements and practicality in roofing work environments.

Wider roof areas would typically necessitate more rigorous fall protection due to the increased risk of falls, thereby explaining why choices that imply widths greater than 50 feet are not suitable for this regulatory exemption.