Fire Safe Fluid Guide

In September 1991, at a food processing plant in Hamlet, N.C. USA, a fire killed 25 workers and injured 50 others. The cause of fire was a failure in the plant's hydraulic system. To replace a defective hose, plant 
maintenance personnel had shut down a conveyor belt which carried chicken parts through 26 foot long deep fat fryer. When the system was restarted, the new hose ruptured. Hydraulic oil under high pressure was 
sprayed onto the fryer, and ignited.

The fire and its aftermath was a reminder that industrial functional fluid systems probably need more attention in industry than they have up to now. Many industrial applications of function fluids involve the use of flammable oils near equipment which generates high temperature as a normal part of their operation. Since many functional fluids need to be under pressure to be useful, a leak in a hose or valve can result in a 
potentially dangerous situation.

Fire resistant fluids can make such systems less susceptible to sudden flash fires when fluid droplets fall onto very hot machinery.


1.0 FIRE RESISTANT FLUIDS
Almost all organic materials can be made to burn under certain conditions. With industrial functional fluids, however, the important consideration is whether they can be ignited by high temperature conditions in and around the systems in which they are used, and if so whether they will continue to burn and thereby spread the fire to other equipment in the vicinity. 

The information contained under different section headings in this guide is applicable in other sections. For example, the information on Fluid Management under the Fire Resistant Hydraulic Fluid section is applicable to all other sections. Likewise, the fire prevention guidelines under the Heat Transfer Section is applicable in all other sections.


2.0 FIRE RESISTANT HYDRAULIC FLUIDS - FRHF
Petroleum based hydraulic oil can catch fire when it is sprayed onto a hot spot or when it is ignited by other fire sources. The use of fire-resistant hydraulic fluids would reduce these risks. 

Fire resistant hydraulic fluids which are classified as HF fluids - are sub-divided according to an international agreement into four groups A,B,C and D. These are correspondingly designated HFA, HFB, HFC and HFD.

Compared with mineral oils, these fluids demonstrate some special characteristics. The following guidelines show how these particular characteristics can be taken into account during project engineering, operation and service. At the same time, the measures necessary when changing an installation over from one fluid to another are indicated and should be observed.


2.1 CLASSIFICATION - ISO 6743/4

2.2 PROPERTIES OF FLUID

Note:
1. All comparisons are broad generalisation. Performance and quality of specific fluids will vary depending on make or manufacturer of fluids.

2. Current technology may have characteristics which overcome the limitation listed, eg- water glycol which has lubricity comparable to mineral oil and phosphate ester.

3. The water content in these fluids is very critical and must be checked regularly. As the water content falls, there is a considerable variation in both viscosity and fire resistance, for example. When topping up, the water should be as pure as possible (deionized).

4. The freezing point of water is below 0oC and as such water containing fluids should not be allowed to fall too far. 

5. Oil separation can occur if the fluid remains stationary, by freezing and thawing, under high shear conditions and also by contamination by acids, alkaline, salts or solvents. Under certain circumstances, re-emulsification can take place by means of a pump and pressure relief valve.

6. Stability can be affected by extreme temperatures which can lead to evaporation of the water and with it a reduction in water content, separation of water and glycols, evaporation of inhibitors and a chemical change in the inhibitors causing resinous substances which cannot be re-dissolved.

2.3 MATERIAL COMPATIBILITY

Key: C=Compatible, NC= Non-compatible, 
S=Satisfactory for short term use, replace as soon as possible with completely compatible elastemers

2.4 CHANGE OVER PROCEDURE

The following procedure is recommended in making the change-over from a petroleum hydraulic oil to FRHF.

1. Drain oil from system completely. Particular attention should be paid to the reservoir, fluid lines, cylinders, accumulators, filters and other equipment where residual oil may be trapped.

2. Clean the system of residual sludge and deposits. Ensure that the paints from the inside of the reservoir if present have been tested and found to be compatible with the FRHF. The use of carbon tetrachloride or other chlorinated metal cleaners should be avoided.

Cleaning should be as complete as existing conditions will permit.

3. Remove or disconnect the filter.

4. Flush the system with a minimum quantity of FRHF. Flush initially by operating at no load or at minimum pressure, then, bring the fluid up to normal temperature and operate all parts. Many users follow the practice of operating on the flush fill for several hours in order to ensure complete circulation. Systems previously filled with fluids other than mineral oil should be flushed with mineral oil before proceeding as above.

5. Drain the flushing charge as completely as possible while it is still warm and without allowing it to settle. This fluid can be retained for further use after suspended solids have settled and residual petroleum oil has separated. With proper attention to removal of suspended contaminants, the flushing fluid can be used in preparing other machines for service.

6. If a filter is used, install a clean filter cartridge. Replace with compatible filter elements. Do not use a highly absorptive filter medium such as activated clay or Fuller's Earth since these filters may alter fluid composition by removing essential additives - with the exception of systems using additive free fluid.

7. Examine pump parts, o-rings, and auxiliary equipment for compatibility with the FRHF in use.

Worn pump parts should be replaced. Leaking pipe joints should be repaired and deteriorated gaskets, seals and packings should be replaced in order to minimise mechanical fluid losses. Cork shaft seals should be replaced if they are present in the system.

8. Reconnect the system and tighten all joints and connections.

9. Fill system with FRHF.

10. Operate at reduced pressure to ensure lubrication of the hydraulic pump; then bring up to standard operating conditions.

During the first few weeks of operation, particular attention should be paid to the filters and inlet screens. They may become clogged by sludge and deposits that have been loosened during the change over procedure. Such blockages may cause pump starvation, noisy operation and high pump wear. Therefore, filter cartridges should be replaced and inlet screens cleaned as often as needed.

2.5 FLUID MAINTENANCE

Improper use of hydraulic fluid can be costly due to system reliability and fluid cost; it may even be potentially dangerous. Following some simple guidelines can improve system reliability, prevent damage and ensure long fluid and system life. These include:

- Store hydraulic fluid drums on their side and keep them dry and cool (preferably under 
shelter).

- Ensure the utmost cleanliness when topping up or renewing the fluid in the system. Use 
clean fluid transfer utensils.

- Pump the fluid through a pre-fill filter into the reservoir and test the fluid frequently and 
regularly.

- Establish fluid change intervals (frequent predictive maintenance fluid testing) so that 
oxidation and fluid breakdown never occurs.

- Prevent fluid contamination at all costs, and use proper air and fluid filtration.

- Prevent excessive fluid heat build up; if required, use cooling or check for design faults.

- Repair all leaks immediately, and use properly trained personnel for the maintenance of the 
system.

- Prior to fluid change (from oil to fire resistant fluids), make sure that components and seals 
are compatible with the new fluid (check with component and fluid suppliers), and ensure 
that the whole system is adequately flushed before it is re-commissioned.

2.6 FLUID MANAGEMENT

Proper hydraulic fluid management is the key to higher productivity and reliability of hydraulic systems. This is especially so in FRHF because the fluid not only must meet the functional performance criteria, it must also meet the fire resistance requirement. 

A typical monthly routine test on FRHF reports the following:

Kinematic Viscosity
Fluid polymerization caused by overheating will cause a rise in viscosity. Dilution with water or contamination with the wrong oil for the application will vary the viscosity. Off-specification supplier oil can also be picked up occasionally.

Water Content
High water content in mineral oils can allow growth of bacteria and fungi in the water phase, rust promotion for ferric components, filter blockages, reduced operating viscosity.

Low water content in HFA, HFB and HFC will reduce fire resistance properties and cause an increase in viscosity and conversely an ingress of water will reduce viscosity and lubricity in a system.

Neutralization Number/ pH
Acidity can rise due to overheating, contamination with water or particulates and ultimately lead to corrosive levels of acid radicles and/or gums in the system.

Colour, Appearance and Odour
Much information can be obtained from physical examination of the fluid. In many instances the information gathered from physical observation may be more important than testing with laboratory equipment.

(The above analysis will determine the chemical condition of FRHF. The system condition however can be determined by one or a combination of the following tests.)

Particulate Count
Particulate contamination is reported as NAS 1638 or ISO gradings. High particulate contamination of any type can cause component wear, filter blockages, premature fluid ageing, reduced fluid performance. Particle counting equipment measures particles from 5 micron in size upwards (0.0001 cm)

Contaminants Identification
Microbiological Tests - Bacteria, fungi and yeast are all capable of growing in the water phase of a lubricant system. Once the type of growth is identified, then the correct dosage and type of biocide can be recommended in order to kill the offending organism/s

S.O.A.P - Measures elements such as Iron, Aluminium, Manganese, Copper (generated as wear metals) for particles sizes less than 5-10 microns. This test was very popular in the past but it is now known that particles generally larger than 10 micron cause more wear damage than small particles. 

Filtergram - Looks microscopically at particles present in the oil, and can predict where they have arisen, e.g. dust entry, fluid additive breakdown., machine wear. A recommendation for corrective action can be taken from this test.

The data collected ought to be trended to provide an insight to the behaviour of the system. This should be part of a predictive maintenance program of the system.

3.0 FIRE RESISTANT COMPRESSOR LUBRICANTS - FRCL

Perhaps one of the least understood hazards facing the compressor user today is the possibility of fires and explosions in compressed air systems. This is especially unfortunate at a time when compressed air is proving its utility in many new applications. Fires can be troublesome and explosions although rare, can be sudden, violent, and extensive. Serious injury and heavy material damage have resulted.

Conventional petroleum lubricated air compressors are subject to carbon build up and lubricant breakdown. Lubricant vapours mix with the compressed air under high temperatures, producing a potential for explosion and fire. The risk depends on the spontaneous ignition condition for the mixture of oil vapour (or mist).

This situation is particularly prevalent in the case of reciprocating compressors which are very widely used throughout industry. Continuous high temperatures in the cylinder during the compression cycle are found to be as high as 260oC on a single stage compressor at a discharge pressure of 100psi.

The "shock" wave produced in the auto-ignition, compresses the coating of oil in the compressor. If the ignition is rapid enough the shock wave may cause the sudden vaporization and ignition of the oil film in the compressor, hence an explosion.

This danger cannot be fully eliminated by devices such as safety valves nor special design nor layout of equipment. Because shock waves build up speed and pressure in cycles, one may fail to actuate a safety device if it passes by while in the low-pressure part of its cycle, yet it may detonate only a short distance beyond.

3.1 PROPERTIES OF FLUID

In reciprocating compressors, FRCL are mainly synthetic fluids either used neat or blends with other synthetic lubricants and/or mineral oil. 

These fluids guard against compressor fire hazards in several ways. The machines when lubricated with mineral oil normally accumulate carbon deposits which are a potential source of valve malfunction leading to fire and explosions. 

Some FRCL are practically deposit-free when used properly. They even scavenge foreign matter and petroleum residues, keeping valves clean. Some show little tendency to vaporize as typified by their remarkably low vapour pressure. Oil vaporizes with relative ease, and is carried downstream from the compressor to form a combustible film in adjacent equipment and air headers, creating fire hazards.

3.2 SYNTHETIC COMPRESSOR LUBRICANTS

The motivation behind the development for many synthetic lubricants has been to extend the useful operating temperature range beyond the limits of mineral oils and reduce the risk of fire.

The temperature and fire resistance characteristics of various synthetic lubricants are listed as 
follows:

Of the synthetic lubricants available for air-compressor cylinder lubrication, phosphate esters have been used primarily because of their high autoignition temperature. 

4.0 HEAT TRANSFER FLUID (HRF) FIRES AND THEIR PREVENTION

Most heat transfer fluids are rated by the National Fire Protection Association (NFPA) Standard 30, Flammable and Combustible Liquids Code of the US.

Both liquid phase and vapour phase systems are used in process heat transfer.

While the organic heat transfer fluid has many advantages, these materials are combustible liquids, and these systems can feed a fire. Such fires can result from a fired heater tube leak, a tube rupture or other mechanical failure. Releases from a vapour system can form an aerosol mist, which can burn explosively in air.

HTF containment in the heat transfer system where there is an absence of combustion air is essential in reducing the risk of HTF fires.

4.1 FIRE TYPES

Industrial fires most often reported in organic HTF systems are those ignited due to surrounding high-temperature environments. These fires include those related to HTF leakage into insulating material and fire from heater tube leakage or ruptures into hot gas-open flame areas.

4.1.1 Insulation Fires 
Insulation-related incidents are some of the most common types involving organic HTF systems. Typically, a leak occurs at a flange or instrument connection and soaks into the pipework insulation (e.g., calcium silicate, Fibreglass, mineral wool). Eventually the saturated insulation is ignited when the circulating fluid and the piping heat the HTF and, in the presence of air, slowly oxidise the fluid. This produces low AIT components which results in a "punking" type fire. This fire can act as an ignition source for other fires.

Leaks are often elusive in hot and fully insulated heat transfer systems. And because of the material properties and the thermal expansion and contraction of the piping system during shutdown, leaks are prone to occur. Without proper maintenance, the possibility of leak development must be taken into account.

Proper design of the piping and insulation system is a must. Primary design criteria should include insulation of a type that is not easily soaked or covered, so leakage will drain away from the system without soaking the insulation.

4.1.2 Tube Leak/ Rupture Fires
Tube leaks and/ or tube ruptures into a hot gas open flame area are often the most damaging from a property and business interruption standpoint. When these failures occur, an ignition source and self-ignition environment are usually immediately available, and there may be a large storage volume of pressurised fuel available to feed the fire.

Tube ruptures/ leaks can occur for several reasons, including over firing, tube flow blockage. 
interruption, fireside corrosion/ erosion, HTF contamination, over pressure, age, design inadequacies, flame impingement, and thermal expansion/ contraction.

Thermocouples can be used to monitor flue gas temperatures, tube metal temperatures or HTF temperatures, and visual checks of the firebox tubes can be made. However, periodic inspection during shutdowns and testing of the HTF system are still needed to protect against this type of hazard incident.

4.1.3 Flash Point Fires
For this fire mechanism to operate, the fluid, the air atmosphere and an ignition source must coexist above a minimum temperature known as the flash point. This condition seldom exists in reasonably designed and operated heat transfer systems with modestly high flash point fluids. Avoiding leakage to the potential ignition sources is a must. Proper selection of pumps, piping systems and adequate maintenance will help minimise these incidents. Relief vents from the HTF systems must be to a safe area.

4.1.4 Process Materials Fires
A fourth category of fires results from HTFs leaking into the process being heated where the process materials are oxidising agents or active catalytic surfaces promoting combustion. Again, mechanical design and maintenance to prevent thermal cracking, corrosion or oxidation of the process materials or HTF are your best protection against this source of fires.

4.2 FIRE CASE HISTORIES 

Case histories as related to the type of fluid, hydrogen-to-carbon ratio, system temperature, area of the fire, fire type, and causes of the fire are presented in Table 1. Table 2 gives a brief description of the events leading to the fire. Table 3 describes what corrective actions were taken, if any. 

Chart 1 represents the types of fire at different hydrogen-to-carbon ratios. All of the insulation-type fires occurred with the highly alkyl hydrocarbon fluids. When the H:C ratio is compared to system temperatures (Chart 2), one finds lower stability, highly alkylated fluids used in the lower temperature systems experienced the insulation fire in the case histories. While not in the customer history sample, there have been insulation fires with highly aromatic HTFs.

When examining the cause of the fires in our population, there seems to be little relation to the H:C ratio or the system operating temperature (Charts 3 and 4). The mechanical failures, system misoperation and the design errors are related more to human judgement, system construction and component selection.

4.3 FIRE PREVENTION

During design, some methods for consideration include: all equipment meeting the prescribed 
standards (see Reference Standards - attached), relief devices installed on all large components, snuffing steam provided on the fire box side of any fired heater, remotely operated (fail safe) valves and automatic pump shutdown incorporated, discharge lines provided on all relief devices, fired heater and other equipment adhering to spacing guidelines, equipment/valving with manual backup of automated controls, insulation materials carefully selected, spiral wound stainless steel flexible graphite-filled flange gaskets used, and electrical equipment designed to prevent ingress of heat transfer mists.

Where ignition sources are present, as in fuel-fired heaters, the ignition source containing equipment should be in an open environment or have high air exchange ventilation to prevent HTF vapour or mist accumulation.

To minimize the possibility of an incident or the consequences of an incident, areas of concern include: complete operation manuals provided with adequate training of all operators, refresher training given to all operators, emergency response team training given, emergency drills conducted, and manual fire extinguisher (Class B) provided with training for personnel for fighting small fires.

4.4 FIRE PROTECTION

Guidelines that may be followed to improve the overall safety of the heat transfer installations 
include the following:

1. The fired heater and other equipment should adhere to the spacing guidelines noted in NFP 30. This document gives guidelines for spacing from property lines and important buildings.

2. Where possible, heat transfer systems should be installed in open structures. Closed structures should have explosion relief construction and adequate ventilation to prevent vapour concentration.

3. The design should consider the benefits of a primary and secondary heating loop to isolate the heat transfer fluid.

4. Automatic, remotely operated (fail safe) valves and automatic pump shut-down should be 
incorporated to prevent the possibility of the system feeding the fire in the event of a tube rupture. This shut-down could be triggered by a low-flow interlock, a low expansion tank level interlock, a high stack temperature interlock, or other acceptable means. Provisions should be provided for pressure relief as required.

5. Automatic sprinklering is recommended. Considerations should include the burner front, relief device discharges, control rooms, furnace openings, heat transfer fluid piping systems and vessels, escape routes, and operating areas.

Suggested guidelines for the protection of new fluid heater installations are as follows:

A. Automatic deluge protection on an area basis (0.3 pm/ft2)

B. Areas requiring the automatic deluge protection to include grade level, burner firing 
level, the three external vaporizer walls (where vaporizers are closely spaced), and 
subsequently levels above the burner level.

C. Manual fire extinguishers available.Class B.

D. Slope grade so run-off is routed away from equipment.

E. Supplement automatic systems with 500 gpm (single fire unit) -- 1,000 gpm (multiple 
furnace) available capacity for hoses.

6. Snuffing steam (or other acceptable media) should be provided on the fire box side of any fired heater.

A commonly used method of preventing fire in the event of tube rupture in fired heaters is to 
supply steam or CO2 as a snuffer into the combustion chamber of the heater. Steam snuffer 
systems should employ a trap to avoid slugging the combustion chamber with water when the system activates or is activated manually. This snuffer system can be automated by the use of an exhaust stack temperature switch, which would energize a solenoid valve and an alarm upon excessive temperature rise, thus automatically flooded the chamber with a fire 
extinguishing agent.

7. Consider remote operation of key equipment/valving with manual back-up of automated controls.

8. Electrical equipment should be designed to prevent ingress of heat transfer mists.

9. Insulation (in areas prone to leakage) should be of a type that cannot become saturated with the fluid. One example would be cellular glass. Care must be taken to verify the insulation material is suited for the system temperature. The piping system should be designed for combustible fluid service at the rated temperature.

10. Discharge lines on all heat transfer fluid relief devices should be :
A. Routed to a safe discharge to atmosphere (not inside a heater room) or routed to an adequate collection system.

B. If necessary, protected with additional fire protection so that the fire hazard is minimized at the discharge point.

4.4 MAINTENANCE AND REPAIR

Key areas which should be checked to minimize loss potential include: HTF periodically checked for contamination and/or degradation, the flame in a fire vaporizer observed for appearance, tubes in a fired vaporizer periodically checked for solids deposition, safely relief devices inspected and/or replaced regularly, critical interlocks tested at least yearly, fire protection equipment tested at regular intervals, piping repairs completed, and all vessels included in a vessel inspection program.

4.5 SUMMARY

While organic thermal liquid HTFs can have advantages over steam and hot gas-direct fired systems, system design and operation must recognize their combustible nature. Particular attention must be paid to insulation and heater fire hazards by proper containment of the HTF in the system. Highly alkylated synthetics and mineral oils appear to be susceptible to insulation fires while aromatic organic HTFs seem resistant to such fires. The absence of flash point fires is often attributable to good safety practices of keeping ignition sources away from the system piping and process units.

Fire loss prevention techniques should address two areas: prevention of the fire, and control and containment should a fire occur. Proper design, personnel training, operations and maintenance, as well as repair procedures, will all help prevent the HTF releases and potential fires. Fire control and containment will be obtained by adequately designed sprinkler systems and snuffing steam, adequate spacing of equipment will appropriate fire-resistant barriers, valving and instrumentation for isolating equipment and/or piping, and properly prepared and equipped emergency response teams.

5.0 TURBINE CONTROL FLUID

An integral part of the operation of most large steam turbine generators is the electro hydraulic control system. In these systems, the hydraulic fluid transfer lines are often near high temperature steam lines. To reduce the hazard of fluid ignition should leakage come in contact with high temperature metal surfaces, the system's manufacturers require a fire resistant fluid to be used. An evaluation program by turbine manufacturers indicated that Phosphate Ester Fluids provide the best overall performance characteristics.

Phosphate Ester Electro Hydraulic Control Fluids are inherently fire-resistant. These fluids will not support combustion or propagate a flame. They have extremely low vapour pressures, giving them high flash and fire points. If ignited, they will generally burn only at the source of ignition and will normally self-extinguish once the source of ignition is removed.

The design considerations, fluid maintenance and management as well as change over procedure of TCF are similar to that of Fire Resistant Hydraulic Fluids.

6.0 MINING EQUIPMENT

Most of the mining equipment using large volumes of fluid are covered in one of the above sections. One major concern regarding Fire Resistant Fluid in a confined area such as a mine, is the toxicity of fumes formed in case of a fire. It is for this reason that most large volume hydraulic supporting system in the mining industry are using high water containing fluids.

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