Why is it crucial to ensure proper ventilation when servicing gas appliances?

Ensuring proper ventilation when servicing gas appliances is crucial primarily to prevent the accumulation of harmful gases like carbon monoxide. Gas appliances, when functioning correctly, produce combustion gases as a byproduct. If these gases are not properly vented, they can build up in the working environment, posing significant health risks, including carbon monoxide poisoning, which can be life-threatening.

Maintaining adequate ventilation allows for the safe dispersal of these gases, ensuring that they do not reach harmful concentrations. This is particularly important when servicing appliances, as any malfunction or incomplete combustion can result in increased production of toxic gases. Proper ventilation helps mitigate these risks, safeguarding both the technician and any occupants in the area.

The other options, while they address relevant aspects of gas appliance operation and servicing, do not emphasize the critical nature of safety and health concerns related to harmful gas accumulation. Thus, option B stands out as the most important reason for prioritizing proper ventilation during service work.