What type of pressure is provided by an SCBA during repairs on a chlorine gas leak?

The correct answer is positive pressure, which is essential for safe operations when dealing with hazardous substances like chlorine gas. Self-Contained Breathing Apparatus (SCBA) operates by supplying air to the user at a pressure higher than the atmospheric pressure. This positive pressure prevents any external contaminants, such as chlorine gas, from entering the breathing mask.

When workers are repairing a chlorine gas leak, it is crucial that they are protected to prevent exposure to harmful gases. By using an SCBA, which delivers air at positive pressure, the system effectively keeps the toxic gas out, ensuring that the worker can operate safely in an environment that may otherwise be dangerous.

The other options, such as atmospheric pressure, negative pressure, or vacuum pressure, would not provide adequate protection, as they either allow for the possibility of contaminant ingress or simply do not meet the necessary safety standards required for working in hazardous conditions.