The LFL (lower flammable limit) and UFL (upper flammable limit) of R1150 were researched experimentally on a self-made test rig according to the Chinese National Standard GB/T12474 under variable temperature and humidity conditions. Results showed that the LFL increased with the decrease of temperature, while the UFL reduced, therefore the flammable range shrank 3.42% from 55 degrees C to 5 degrees C. Another group of experiments had been carried out to test the influence of humidity on the flammable limits of R1150 at 25 degrees C, which presented that the LFL increased less than 0.1 and UFL reduced 0.87 in volume fraction when humidifying the air to 42.4% (relative humidity). At the same time, a new method of estimating the LELs of general hydrocarbons was presented and the relative deviation between the calculated value and experimental datum of R1150 was as small as 0.88%. On that basis, the influence of temperature on the LFL of R1150 was estimated by adding parameter enthalpy into the computational formula, the relative errors lay in 0.35-2.54% at the temperature range from 5 degrees C to 55 degrees C. The research achievements can benefit for utilizing the hydrocarbons refrigerants in variable temperature and relative humidity. (C) 2013 Elsevier Ltd. All rights reserved.