Insulation classes and type of materials than can be used in NORSOK M-004.

Definition of different insulation classes

When doe a fire occur?

In order for a fire to occur we must have in the same place, at the same time and in the right mixture:

• Flammable material
• Oxygen
• High enough temperature

Fire propagation can be divided into three phases:

• The initial phase
• Flame phase
• Cooling phase
  

The initial phase

The fire is spreading slowly within a small, confined area. The speed of fire development depends on what type of material is burning. A fire in this phase can normally easily be stopped using fire extinguishing equipment, removing the oxygen supply or possibly cooling or removing the flammable material. To avoid major fire damage to materials, fire extinguishing must begin during this phase.

Flame phase

The fire begins to spread to other materials and there is an over-ignition. The fire continues to form flammable gas that is not burned. Without renewed access to oxygen, the fire will die out, while with renewed access to oxygen, and especially at rapid rate, the fire may develop explosively. The room will get overheated.

Cooling phase
When all the flammable material has burnt the cooling phase will start. Residue of burnt material will simmer and the temperature will slowly sink. (see illustration below, phases as a function of time and temperature).

The purpose of fire insulation is to reduce heat supply and ensure that the temperature of pipes, tanks and equipment is lower than the specified critical temperature for a given fire scenario. If the fire incident and critical temperature are not specified, then the temperature should be set at 400°C in a hydrocarbon fire situation, with a duration of 30 minutes in accordance with ISO 834 (all parts).

Normally we distinguish between two different fire scenarios:

• Pool fire - the temperature quickly reaches above 1100 °C.
• Jet fire (Gas) - the temperature reaches 1200-1500 °C.

In both types of fires, hydrocarbons burn and the temperature rises quickly to approximately 1000°C.

Fire insulation is normally carried out to ensure the integrity of the installation or of the plant until the active fire systems are enforced, however, one should not include the effect of this active system when calculating the need and amount of fire protection.

Materials and methods used for fire insulation must be tested and approved. The fire testing shall ensure that all important and relevant workmanship details are documented and followed. For penetrations, certification requirements (certificates) are specified for the product after completion of testing. Testing should be carried out in accordance with international testing procedures:

• Jet fire tested according to ISO 22899
• ISO 834 is used for testing products with oil/pool fire requirements
• IMO RES. A. 754(18) is used for testing of products requiring cellulosic fire

A DAL shall describe the toughest or most serious random load a system should be able to withstand during a specific time in order to satisfy the predefined risk acceptance criteria. The dimensioning load shall not result in loss of safety features or local escalation of the incident. Fire and explosion are part of the loads defined as DAL.

The main tasks of a fire cell is to:

• Ensure that a fire or explosion does not spread into a surrounding area
• Shall as a minimum divide the main areas (living quarter and process area)
• Divide/separate areas with important safety functions (control rooms, electro room, etc.)
• Divide/separate areas with high fire risk (process area) from other areas
• Remain intact in event of a fire

In a fire test a test specimen is exposed for temperatures corresponding to the time-temperature curve for a hydrocarbon fire or a cellulosic fire. The specimen is tested in a closed oven. It should resemble as far possible the construction intended to be used (ISO 834-1). When the test specimen cannot be tested in real size, it shall be in accordance with the test standards for each element.

A standard time-temperature curve for a hydrocarbon fire is an even curve drawn through the following oven temperature (in accordance with ISO 834.1):

Standard time-temperature curve for a cellulosic fire with an even curve drawn through the following oven temperature (in accordance with IMO A.754(18)):

Fire loads
The term fire load is explained in most standards as the sum of radiation and convective exposure of an object, in other words, a total load to which an object can be exposed.

Fire loads vary depending on fuel, access to oxygen, radiation from the environment, flow conditions and the amount of fuel. Units are in kW/m² (kilowatt/m²). Heat fluxes up to 450 kW/m² have been measured.

Point or local maximum fire load:

• When a point or small area is exposed for maximum heat exposure
• The maximum heat exposure decides failure temperature on the metal
• Only has marginal influence on the total fire load in the relevant part of the process

Local/global average fire load

• The average heat flux which a significant part of the process or structure is exposed.
• Will have an impact on fire load in the relevant part of the process

How much can materials withstand?

Steel loses its bearing strength quickly when heated:

• 350°C: Critical temperature for pre-stressed concrete
• 500°C: Critical temperature for construction steel. Strength approximately half of otiginal value
• 1000-1200°C: All load bearing strength is lost (new analysis shows increased load bearing strength relative to steel temperature up to 1200°C)

Aluminium will withstand less heating:

• 200 – 250°C: Critical temperature

Concrete is a poor heat conductor. Rapid temperature fluctuations lead to delamination. Most damage occurs on fresh and damp concrete. Rebar decreases in strength, depending on time, temperature, and thickness of concrete covering. Pre-stressed concrete is most critical.

ISO 834 regulates fire testing of structures, to determine fire resistance contribution of the various passive fire systems used. ISO 834 is built up as follows:

• ISO 834-1: General requirements
• ISO 834-3: Commentary on test method and guide to the application of the outputs from the fire-resistance test
• ISO 834-4: Specific requirements for loadbearing vertical separating elements
• ISO 834-5: Specific requirements for loadbearing horizontal separating elements
• ISO 834-6: Specific requirements for beams
• ISO 834-7: Specific requirements for columns
• ISO 834-8: Specific requirements for non-loadbearing vertical separating elements
• ISO 834-9: Specific requirements for non-loadbearing ceiling elements
• ISO 834-10: Specific requirements to determine the contribution of applied fire protection materials to structural steel elements
• ISO 834-11: Specific requirements for the assessment of fire protection to structural steel elements
• ISO 834- Section 1, specifies test method for testing of fire loads for various building parts when these are exposed to standard fire exposure.
  ISO 834 -Section 10 describes the performance criteria for loadbearing, integrity and insulation capabilities as follows:
  • Loadbearing: Deflection and contraction in the sample cannot exceed certain values. These are specified as a function of dimensions on the sample.
  • Integrity: It is considered a violation of integrity if a cotton piece is ignited on the unexposed side, or there are gaps of a certain size in the sample, or if there are persistent flames on the unexposed side.
  • Insulation capability: The average temperature rise on the unexposed side of the sample should not exceed 140°C and the maximum temperature increase should not exceed 180°C at any point.

Materials used in class H and A fire divisions shall be tested by an international or national recognized laboratory or test institute. Penetrations in fire cells, including materials and assembly method, shall be similar to those used during testing.

Penetrations must not reduce the strength, integrity or insulation properties in a fire cell.

The steel frame (sleeve) can be made of carbon steel, galvanized or rust-resistant steel, regardless of the steel quality used when testing. The sleeve shall be welded to the test set-up. If bolted to the test set-up, the sleeve can be either bolted or welded. Sleeves that have been tested symmetrically should be mounted with approximately equal parts on either side of the fire cell.

Penetrations in a fire cell shall mounted in the same way and with the same type of insulation in the sealing used during the laboratory fire test. However, penetrations of the fire insulation of bulkheads and decks can be of any approved type.

Penetrations in fire cells that have been tested with exposure only on one side must be mounted in a similar way.

Penetrations in fire cells that are mounted in both deck and bulkhead shall be tasted for both types of cells, and in addition, for single and multiple penetrations. The smallest and largest sizes (length x width, cross-sectional area or diameter) shall be tested. Sealing of pipe penetrations larger than those tested is not accepted.

Manufacturers of sealing materials shall provide typical installation drawings that show all installation restrictions carried out during the test. These drawings shall be referenced on the type approval certificate.

Installation drawings for all products to be used shall be included in the penetration dose. The drawings shall contain at least the following information:

• installation limitations
• smallest and largest frame dimension (sleeve)
• installation symmetry
• smallest and largest pipe diameter
• minimum distance between pipes (multiple)
• minimum distance between pipe and sleeve
• side for fire exposure

There may be other requirements that must be emphasized in addition to those for a fire cell.

Consideration to choosing a solution must be taken if a penetration is located in an area where a jet fire may occur. Similarly, when a penetration is in an area with defined explosion loads, consideration must be taken into when selecting a solution. If there are additional requirements for jet fire or explosion resistance, then the properties of products shal be documented with respect to dimensional loads. In some cases, there are requirements for penetrations in a fire cell to be gas- and watertight.

Method for determining dimensioning explosion loads. Before determining the explosion loads, the consequences of an explosion considered unacceptable to the facility must be determined. Such consequences may include:

• Total breakdown of the construction
• Break or unacceptable deformation of explosion barriers
• Unacceptable damage to equipment due to deformation of the deck
• Unacceptable increase in the severity and intensity of the accident due to deformation of equipment containing hydrocarbons
• Unacceptable damage to safety equipment or safety systems that shall function after an explosion

The explosion load shall be determined on the basis of a conservative sample of a specific number of scenarios.