## 4 Results and Discussion
In the first few minutes of the measurement (Figure 2), an increase and then a decrease in the carbon monoxide concentration in the garage was noted, which is caused by starting the cold combustion engine of the car. Starting a cold engine generates a local increase in carbon monoxide concentration, which is caused by the low initial fuel combustion temperature in the engine [41]. The trends in the carbon monoxide concentration changes in the garage (Figure 2), with the ventilation both on and off are similar to the trends in carbon monoxide concentrations presented in the publications [9; 10; 19]. The value of the carbon monoxide concentrations depends primarily on the number of air changes in the garage, the size of the internal combustion engine, and additional optional filters located in the car's exhaust system [19]. In the case of multi-car garages, the carbon monoxide concentration in the room where the cars are parked depends primarily on the current number of parked cars [13]. Due to the high traffic of cars in multi-car garages, the trends in carbon monoxide concentration do not stabilize [13], as in the case of single-car garages in single-family buildings. It should be emphasized that in the garage examined, the only source of carbon monoxide was the combustion engine of a passenger car. In garages, additional sources of carbon monoxide may be boilers [18], power generators [19] and cigarette smoking [42]. Figure 1: Dependence of average hourly and maximum carbon monoxide concentrations as a function of the number of air changes for measurement series with ventilation turned on. Figure 3 shows the impact of opening the external garage door on the carbon monoxide concentration in the garage, when the combustion engine of a passenger car is running. The car was parked with its back to the garage door. In the first interval (1) the engine was turned off and the garage door was open. During this period, the carbon monoxide concentration was 0 ppm. After six minutes, the car engine was turned on and the carbon monoxide concentration in the next six-minute period (2) was approximately 14 ppm. After closing the garage door, the carbon monoxide concentration began to rise rapidly (3) and after another 8 min (3) it reached 290 ppm. Twenty minutes after the start of the experiment, the garage door was opened and the engine was turned off, which resulted in a sharp drop in carbon monoxide concentration to zero in the 27 th minute of the experiment. The test  
Figure 2: Carbon monoxide concentration as a function of time—comparison with the model. results (Figure 3) show how important it is to open the garage door before starting the car's combustion engine. The basic, commonly used and recommended, means of protection against carbon monoxide poisoning are carbon monoxide detection sensors combined with an alarm. When the acoustic carbon monoxide alarm goes off, leave the room quickly [15]. Based on the research conducted, an automatic signalling and control system for carbon monoxide in garages of single-family houses was proposed (Figure 4). The system consists of a regulator (1), a carbon monoxide sensor (2), an exhaust fan (3) connected to the exhaust ventilation duct (4), an acoustic alarm (5), and an electric actuator (6) that opens the garage door (7). If a significant concentration of carbon monoxide is detected by the carbon monoxide sensor (2), the fan (3) is turned on at the maximum rotor speed, the alarm is activated by the acoustic generator (5) and the garage door (7) opens using the electric actuator (6). Figure 4: Schematic diagram of garage protection system against carbon monoxide: 1—regulator, 2—carbon monoxide sensor, 3—exhaust fan, 4—exhaust ventilation duct, 5—acoustic signal, 6—electric actuator, 7—garage gate. Figure 3: Carbon monoxide concentration as a function of time—the impact of opening the garage door on the carbon monoxide concentration when the combustion engine in a car is running.