A nonflammable gas mixture for plastic limited streamer tubes

The gas mixtures presently used in plastic limited streamer tubes ("Iarocci tubes" or LSTs) have a high hydrocarbon content and are very flammable when mixed with air, posing a potential safety hazard in modern large underground experiments. The SLD Warm Iron Calorimeter group has therefore made an extensive investigation of nonflammable ternary mixtures based on CO2. Ar and various hydrocarbons. We present here brief results of this research. In particular, we describe a detailed study of a nonflammable gas mixture (2.5% Ar: 9.5% iC4H10: 88% CO2) which indicates that this mixture has properties comparable to those of the two commonly used gases (25% Ar: 75% iC4H10 and 21% Ar: 37% nC5H12: 42% CO2) and could successfully replace these mixtures in LST-based tracking devices and hadron calorimeters.