Is sewer gas dangerous? A quiet nightmare occurs daily in our older condos that affects our health, especially in South Florida, where we have older condos. The nightmare is old sewer lines made of cast iron pipe that are degrading and, at best, creating hairline cracks, which permit the infiltration of harmful gases and bacteria into our living areas. Sewer gas exposure can make you sick; exposure to these gases can cause headaches, dizziness, memory loss, poisoning, and asphyxiation. In large enough amounts, there is even a risk of fire or explosion.it is important to take any odd smell coming from your sewer seriously, especially in condos where the sewer lines run vertically inside the walls; one of the gases released in the sewer is hydrogen sulfide (H2S), which is slightly denser than air, and a mixture of H2S and air can be explosive. symptoms of exposure to sewer gas