chemical structure, and thermal stability among other factors. Hence, these values
can vary depending on the FR and polymer being tested, as we shall describe in the
following sections. This method, first introduced by Fenimore and Martine in 1966,
is now standardized in the USA (ASTM D2863) and internationally as well (ISO
4589). The LOI value generally defined as the ratio between consumed oxygen
volume divided by total volume of oxygen and nitrogen gases in atmosphere, i.e.,
LOI = [O 2 ]/[O 2 ] + [N 2 ] Â 100.
On the basis of the LOI values, we can predict the flammability of a material.
Usually, ambient atmosphere contains 21% oxygen. Therefore, materials with LOI
values less than 21% are considered combustible, while those with LOI > 21% are
categorized as self-extinguishing, because these materials cannot undergo combustion atmospheric temperature without any external energy, such as temperature
or a light spark. Therefore, a high LOI value indicates better FR activity. In the ISO
4589 method, the specimen is placed at the center of the top of the chimney.
A mixture of gases flows upstream via this chimney and is homogenized by passing
through layers of glass beads for purging the column over 30 s; the top of the
specimen is ignited like a candle and the consumed oxygen volume is measured.
3.3 Underwriters Laboratory-94 (UL-94 V)
This test is useful in investigating and classifying the FR level of different materials.
It is based on time taken by the flame to spread and the ability of the material to
resist dripping. In particular, it is critical to understand the FR activity of plastic
materials in applications where flame resistance is necessary. The UL-94 test
consists of a set of tests approved by the Underwriters Laboratory and materials are
classified as V-0, V-1, V-2, etc. depending on simple vertical combustion; if a
material burns slowly or self-extinguishes without dripping, then it is assigned the
highest ranking in the UL-94 test. This test method is most commonly used for
evaluating the ignitability and flame spread of a vertical sample exposed to a small
flame. Flame is applied to the bottom of a sample vertically hung from the top of the
burner and the minimum sample size is 10 mm. The sample is exposed to the flame
for 10 s and removed; the after-flame time, t 1 , which is the time period required for
the flame to terminate or stop is measured. After the flame dies down, the sample is
exposed to a flame once again for another 10 s and the after-flame time t 2 is noted
together with the after-glow time, t 3 (the time required for the glow to disappear).
The distance between the burner and specimen should be constant during the
experiment. The standard specifies that five specimens must be tested and based on
t 1 , t 2 , and t 3 , the specimens can be categorized as V-0, V-1, and V-2 as shown in
Table 3.1 [2].
3.2 Limiting Oxygen Index (LOI)
13
can vary depending on the FR and polymer being tested, as we shall describe in the
following sections. This method, first introduced by Fenimore and Martine in 1966,
is now standardized in the USA (ASTM D2863) and internationally as well (ISO
4589). The LOI value generally defined as the ratio between consumed oxygen
volume divided by total volume of oxygen and nitrogen gases in atmosphere, i.e.,
LOI = [O 2 ]/[O 2 ] + [N 2 ] Â 100.
On the basis of the LOI values, we can predict the flammability of a material.
Usually, ambient atmosphere contains 21% oxygen. Therefore, materials with LOI
values less than 21% are considered combustible, while those with LOI > 21% are
categorized as self-extinguishing, because these materials cannot undergo combustion atmospheric temperature without any external energy, such as temperature
or a light spark. Therefore, a high LOI value indicates better FR activity. In the ISO
4589 method, the specimen is placed at the center of the top of the chimney.
A mixture of gases flows upstream via this chimney and is homogenized by passing
through layers of glass beads for purging the column over 30 s; the top of the
specimen is ignited like a candle and the consumed oxygen volume is measured.
3.3 Underwriters Laboratory-94 (UL-94 V)
This test is useful in investigating and classifying the FR level of different materials.
It is based on time taken by the flame to spread and the ability of the material to
resist dripping. In particular, it is critical to understand the FR activity of plastic
materials in applications where flame resistance is necessary. The UL-94 test
consists of a set of tests approved by the Underwriters Laboratory and materials are
classified as V-0, V-1, V-2, etc. depending on simple vertical combustion; if a
material burns slowly or self-extinguishes without dripping, then it is assigned the
highest ranking in the UL-94 test. This test method is most commonly used for
evaluating the ignitability and flame spread of a vertical sample exposed to a small
flame. Flame is applied to the bottom of a sample vertically hung from the top of the
burner and the minimum sample size is 10 mm. The sample is exposed to the flame
for 10 s and removed; the after-flame time, t 1 , which is the time period required for
the flame to terminate or stop is measured. After the flame dies down, the sample is
exposed to a flame once again for another 10 s and the after-flame time t 2 is noted
together with the after-glow time, t 3 (the time required for the glow to disappear).
The distance between the burner and specimen should be constant during the
experiment. The standard specifies that five specimens must be tested and based on
t 1 , t 2 , and t 3 , the specimens can be categorized as V-0, V-1, and V-2 as shown in
Table 3.1 [2].
3.2 Limiting Oxygen Index (LOI)
13