How to choose the type of fire detector

The fire is affected by the type of combustible material, the nature of the fire, the distribution of combustible materials, the conditions of the fire site, the weight of the fire load, the supply of fresh air, and the ambient temperature. Generally, the occurrence and development of fire are divided into four phases:

Early period: The fire has not yet formed, only a certain amount of smoke has appeared, basically no material damage.

Early: The fire began to form, and the amount of smoke increased and the temperature rose. Fire has begun to appear, causing less damage.

Mid-term: The fire has already formed, the temperature is high, and the combustion accelerates, resulting in greater material losses.

Late: The fire has spread.

Based on the above analysis of fire characteristics, the detector selection is as follows:

Smoke detectors are very effective as early and early warnings. Any important site that requires low fire damage has a smoldering stage at the beginning of the fire, ie a large amount of smoke and a small amount of heat, with little or no flame radiation, such as the ignition of cotton and hemp fabrics. Suitable for use.

Unsuitable for all fields: smoked places in normal circumstances, often with solids such as dust and water vapor. Locations where liquid particles are present, rapid fire, very little smoke, and explosive situations.

The application of ion smoke and photo-electric smoke detectors is basically the same, but it should be noted that they have different characteristics. Ion smoke detectors are also sensitive to tiny particles that are invisible to the human eye. For example, paint can be detected by humans and the taste of burned coke can cause detectors to move. Even molecular molecules with large molecular weight can cause detectors to occur. The action, when the wind speed is too large (for example, more than 6m/s) will cause the detector to be unstable, and the life of its sensitive components is shorter than that of the photoelectric smoke detector.

For fires with intense flame radiation and only a small amount of smoke and heat. Such as light metals and their compounds fire, should use photo-sensitive detectors, but should not be used in places where there is smoke before the flame spread and the detector's lens is easily contaminated, blocked and used by electric welding, X-rays and other places.

Temperature-sensitive detectors are very effective for early (early, mid-term) warnings of fire formation. Because of its stable work, it is not disturbed by non-fire smoke fumes. Temperature-sensing detectors can be used where smoke detectors cannot be used, allowing certain material losses, and non-explosive conditions. It is especially suitable for places where there is a lot of dust, smoke, water vapor, and rooms where the relative humidity is often higher than 95%, but it is not suitable for places where smoldering fire may occur.

The constant temperature type allows a large change in temperature and is relatively stable, but the damage caused by the fire is large. It should not be used in locations below 0 degrees Celsius.

The differential temperature type is suitable for early warning of fire, and the damage caused by fire is small. However, if the fire temperature rises too slowly, it will not respond and be missed. Differential temperature type has the advantage of differential temperature type and is more reliable than differential temperature type. Therefore, it is best to use a constant temperature detector.

A variety of detectors can be used in combination, such as a combination of smoke detectors and temperature detectors, should be used in large and medium-sized computer room, clean plant and fire shutter facilities and other places. For the rapid spread, a large number of smoke and heat generation, fire with flame radiation, such as oil burning, should use three kinds of detectors.