Gas Monitoring Project

Monitoring Levels of O2, CO, CO2, H2S and HC in Caves in the United States

A gas monitoring project was started in 2010 to better understand the 'typical' levels of various gases within caves in relation to time of year and other weather events. Gases of interest to this study include carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), oxygen (O2), as well as a mixture of hydrocarbons (HC). CO and H2S are measured in parts per million (ppm) whereas the remaining gases are measured as a percent. Potential uses of this data include understanding the effects of oxygen/CO2 levels on human performance in caves; of increasing understanding of outgassing mechanisms for understanding water chemistry; of location of more cave or entrances in larger systems; and of the effect of different gas levels on the biology and microbiology of caves.

The gas monitors are allowed to equilibrate with the outside air for 5 minutes before measurements are taken and they are placed in a hardbox and carried into the cave for monitoring. Typical outside readings are O2: 20.9, CO2: 0.04 and the remaining gases are 0. The devices are left in the 'on' position so to keep a 'site calibration' active. At time of testing, the box is opened and the devices propped up in the box. They are set upwind of analysts and other cavers for 5 minutes before readings are recorded.

The number of times a cave is visited and the number of readings in each cave is left up to the analysts in charge of the study. Due to the sensitivity and privacy issues with certain caves, a cave code is sometimes used instead of a cave name. This allows us to upload the data for that cave, without the landowner worrying about attracting unwanted visitors. An example cave code may be CIN001. C stands for cave, IN is for Indiana and 001 is the first cave in Indiana that was tested. Please do not bother contacting us and asking for cave locations or the name of a cave if a cave code is placed on the website. All such inquiries will be deleted.

Two gas monitors were obtained from Crowcon (, a portable Gasman for CO2 and a Tetra 3 for the remaining gases. This was made possible by the generous donations from the Bloomington Indiana Grotto, Central Indiana Grotto, Indiana Karst Conservancy, National Cave Rescue Commission Central Region and the Richard Blenz Nature Conservancy. Continued donations are always welcomed to help maintain monitors and calibration equipment and fund further research. Please contact Jess Deli at Jess.Deli14(at) gmail (dot) com for more information or questions/comments about this study.

Current monitoring data can be accessed by clicking here. Options for sorting and searching data will be added soon.