The specific properties, which are checked for various Flame
Retardant Smoke characteristics are evaluated as per norms of prevalent
international specifications. Every customer decides its own set of
requirements and HMT are in a position to offer a wide range of PVC power
cables & electrical power cables to suit these requirements and cover
the needs of particular application economically. These tests are to be
carried out apart from those physical & electrical tests to evaluate the
cable parameters specified in the standards to which it is manufactured.
Following special tests are most commonly
carried out at present on HMT - PVC FRLS cables.
| Oxygen and Temperature Index Test |
| Smoke Generation or Light Obscurtion
Test |
| HCL Gas Emission Test |
| Flammability Tests |
Smoke Generation Test
Optical method is most practiced to measure the amount of smoke generated
while burning the sample. A fixed dimension sample of material is put to
flame of specified intensity for 4 minutes and the percentage obscuration on
an optical path is measured a 15 seconds interval. A graphical plot of such
measurements evaluates the average smoke density. This area integration
method is only the quantitative indication of smoke generation by the PVC
compound.
The test is generally carried out as specified in ASTM-D-2843 standard.
Flammability Tests
All other tests mentioned are generally carried out on the materials to
ascertain basically the components, which have certain bearings on the fire
resistance characteristics of the cables. These results contribute to select
a proper formulation for a particular application.
There are certain tests, which are carried out on the completed cable
manufactured with such compounds, in which the cable samples are subjected
to flames in different conditions. The method and duration of such flames
vary to a large extent.
The flame medium is generally LPG in the first three tests methods and
Ethnol in the third method.
The extent of damage to the cable under these tests gives an indication of
the behaviour of these cables in actual fire conditions and gives a measure
of fire-resistance in actual conditions.
HCL Gas Emission Test
All PVC Compounds when decomposed due to fire emit gaseous fumes, which are
basically corrosive in nature. This is entirely due to the ingredients used
in the formulations. These fumes, if containing higher amounts of corrosive
gas i.e. Hydrochloric Acid Gas, may damage various instruments and
equipments in the vicinity of fire. More and more stress is being given
these days to control this content in reasonable limits.
A sample of cable compound is subjected to controlled rate of heat for a
certain period and the decomposed gases are collected in alkaline solutions.
Such alkaline medium is then analysed to estimate the HCL evolved.
Oxygen and Temperature Index Tests
Oxygen index is the measurement of oxygen content at which the vertically
held sample when ignited ceases to burn off its own within 3 minutes. This
is a relative measure of combustion resistance of materials in the context
of atmospheric oxygen.
Temperature Index is the temperature at which the vertically held sample
ceases to burn off on its own within 3 minutes at an Oxygen concentration of
21% i.e. atmospheric air.
These tests are generally carried out as specified in ASTM-D-2863 Standard.
This is carried out as specified in IEC-754-1 standard.