More about this air monitoring:

The device used to monitor the air near the Drugmand site was a portable chemical detector. In addition to measuring Volatile Organic Compounds (VOC), it detects Hydrogen Sulfide (a toxic gas), combustible gases (LEL), oxygen displacement / enrichment, and carbon dioxide. LEL stands for Lower Explosive Limit. These are the spikes you see on the graphs from the air monitoring at the Backus residence, which is about 1,600 feet from the Drugmand frac activities.  The readings tell you what percentage of the air is flammable by actually burning it as it draws air through the monitor. Unfortunately, this monitor does not tell you what type of combustible gas it is, pure methane or perhaps, in our area of wet gas, a methane/heavy hydrocarbon blend.  If it were pure methane in the atmosphere, when the concentration reaches 5.1%, an explosion can occur if there is an ignition source. Other gases have different explosive levels.

The reason this data is so alarming is that the levels of combustible gas(es) exceeded 5.1% in the ambient air on the back patio of an occupied residence.  If there had been an ignition source, the conditions were right for an explosion (like what happened at the Chesapeake well site in Avella, Pa which then ignited the condensate trailers and the Atlas Energy well site in Hopewell Township that ignited the frac pit). Some would like us to believe that the public would not likely be exposed to conditions such as these and that well sites are placed at an adequate distance from homes, schools, and other dwellings. This data indicates otherwise. The location of the Drugmand well pad from the Backus home is about 1,600 feet, well over the 200 feet specified in the PA Oil & Gas Act. 

Typically, LEL monitors are used by workers in enclosed spaces or as entry pre-screening. The action would be to evacuate and ventilate when LEL levels exceed 5%. It's unheard of to have levels like this in the ambient air.