Methane leaks at a fracking site near Blackpool have raised concerns about the capacity of the industry to produce gas without harming the environment.
Cuadrilla reported four spikes in methane above levels set by authorities since it began its controversial operation in October.
The largest event saw concentrations of the climate-warming gas rise to around 15 times higher than normal background levels.
Workers attempted to burn the gas as they released it from the well, but it failed to catch light and was released into the air.
Venting unburned methane at the site is banned by the Environment
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