Which of the following is not a permissible environment for storing medical gas cylinders?

Storing medical gas cylinders near heat sources is not permissible due to the potential risk of pressure increase and chemical reactions that can occur when gases are exposed to high temperatures. Medical gases, particularly those under pressure, can become dangerous if subjected to heat, leading to potential explosions or cylinder failure.

In contrast, storing cylinders in a ventilated and dry area is considered safe, as it helps to prevent condensation and corrosion while ensuring that any leaks can dissipate safely. Keeping cylinders in an upright position is necessary for their stability and to avoid damage to the valve or the cylinder itself. Lastly, keeping medical gas cylinders away from flammable materials minimizes the risk of fire hazards, as any leaks could create a combustible atmosphere. Each of these practices is crucial for maintaining safety when handling and storing medical gas cylinders.