Combustible gas is dangerous if the concentration accumulates in such a way that there is a danger of explosion. This level is called the lower explosion limit (LEL). The HF500 detector sounds an alarm when the gas concentration reaches 10% of the lower explosion limit (10% LEL). 

• with green LED for recognition activation
• with red LED and acoustic signal when gas is detected
• automatic reset when gas disappears
• in the event of an alarm, the acoustic signal can be switched off for 5 minutes, if gas is still present after 5 minutes, the acoustic signal will sound again
• with yellow fault LED, this indicates that the HF500 needs to be replaced
• with test button for monthly test
• recommended replacement date shown on the front