In case of a failure in the air brake system, what is the recommended immediate action?

When faced with a failure in the air brake system, engaging the emergency brake is the recommended immediate action. This action allows you to engage a separate system designed specifically for emergencies. The emergency brake is typically a dependable mechanical system that can operate independently of the air brake system, providing an essential backup to help slow down or stop the vehicle safely.

In scenarios where the air brakes are compromised, utilizing the emergency brake can prevent potential accidents caused by loss of braking power. It's crucial to allow the emergency brake to take over to maintain control of the vehicle under adverse conditions.

The other actions, while they may seem like options in the heat of the moment, can lead to dangerous situations. Increasing speed could exacerbate the problem, making it harder to control the vehicle. Holding the brake firmly might not be effective if the air brake system has failed, and pulling over to the side of the road may not be feasible or safe depending on the circumstances and your current speed and position. Hence, engaging the emergency brake is the most effective and immediate response to ensure safety.