The Pittsburgh Post-Gazette has an interesting (brief) history of the issue of pre-emption and natural gas concerns in Pennsylvania. Regarding natural gas distribution systems in the late 1800s: "A Pittsburgh Daily Post editorial, 'Death In The Streets,' warned that 'Save in a state of war we don't believe any large city in the world was ever in a more perilous situation than Pittsburgh is today owing to the dangers of natural gas explosions.' Protest meetings were held throughout the city and the Court of Common Pleas, on request of the city, appointed a commission to investigate what safeguards were required to end the risk of explosions."
The more things change, the more things stay the same ...