ATmospheric EXplosion regulations were introduced as part of the harmo- nization of European regulations for such industries as mines and paper mills, where explosive atmospheres occur; the engine and vehicle test industry was not explicitly identified within the wording, therefore the European automotive test industry has had to negotiate the conditions under which test cells may be excluded where conformity would make operation impossible. As with all matters relating to regulation, it is important for the local and industrial sector-specific interpretation to be checked. The regu- lation classification of zones is shown in Table 4.2. Areas classified into zones 0, 1, and 2 for gas–vapor–mist must be protected from effective sources of ignition.
As has been determined over many years, secondary explosion protection measures such as using EX-rated equipment (even if it was available and in many cases it is not) in the engine test cell makes little sense since the ignition source is invariably the engine itself. Therefore, it is necessary to use primary
TABLE 4.2 ATEX Designation of Zones in Which Gas, Fuel Vapor, and Oil Mist May Form an Explosive Mixture
USA Divisions
ATEX Zone Designation
Explosive Gas
Atmosphere Exists Remark Zone 0 Continuously, or for
long periods
>1000 h/year
Division 1ẳZones 0 and 1
Zone 1 Occasionally 10e1000
h/year Division 2ẳZone 2 Zone 2 For a short period only <10 h/year Chapter | 4 Powertrain Test Facility Design and Construction 81
explosion prevention methods that prevent the space from ever containing an explosive atmosphere covered by ATEX.
These primary precautions, which cover both gasoline- and diesel-fueled beds without distinction, are certified in Europe by the relevant body TU¨F and are:
l The cell space must be sufficiently ventilated both by strategy and volume flow to avoid an explosive atmosphere.
l There has to be continuous monitoring and alarming of hydrocarbon concentration (normally “Warning” at 20% of lower explosive mixture and “Shutdown” at 40%).
l Leak-proof fuel piping using fittings approved for use with the liquids contained.
l The maximum volume of fuel “available” in the cell in the case of an emer- gency or alarm condition is 10 liters.
With these conditions fulfilled, the only EX-rated electrical devices that need to be included in the cell design are the gas detection devices and the purge extraction fan.
In the USA the treatment and classification of “hazardous locations” such as engine and vehicle test cells are defined in the National Electrical Code (NFPA70). Like most regulations having relevance to our industry, parts of the code are subject to local interpretation by the “authority having jurisdiction”
(AHJ), who may be a fire marshal or city planning officer.
The code often refers to the “adequate ventilation” and “sound engineering judgment” being required in classification of industrial spaces. Best and usual practice in the USA often uses changes-per-hour figures in classified zones.
In engine test cells subfloor trenches and in areas up to 1800 above the floor
“where volatile fuels are transferred” require specific ventilation flows.
In general the resulting classifications give similar air flow requirements to European practice, but close working with the local AHJ is advised from the inception and initial planning of any test facility.
Refer to Chapter 6 for a discussion of detailed design strategies of venti- lation systems compliant with ATEX regulations.
Fire Stopping of Cable Penetrations in Cell Structure
Where ventilation ducts, cables, or cable trunking break through the test cell walls, roof, or floor they must pass through a physical “fire block” to preserve the one-hour minimum fire containment capability. All wall penetrations carrying cables between control space and cell should be, as a minimum, sealed by using wall boxes having “letterbox” brush seals in steel wallplates fixed on either side of the central void, which is then stuffed with intumescent fire- stopping material. However, poor maintenance or incomplete closure of these firebreaks, commonly caused by frequent installation of temporary looms, can
allow fire or the pressurized extinguishant, such as CO2, to escape explosively into the control room.
A hole in the control room wall loosely stuffed with rag not only compromises the building’s fire safety, but may also invalidate insurance.
Alternatively, the more robust Hawke GlandÔboxes may be used; these devices provide rigid clamping of the individual cables and although the fire block can be disassembled and extra cables added, it is not particularly easy to use after a year or more in service, so it is advisable to build in a number of spare cables at the time of the initial closure.
Intumescent materials are widely used to “fire-stop” test cell penetrations.
Often based on a graphite mixture, such materials swell up and char in a fire, thus sealing their space and creating a barrier of poor heat conduction. Intu- mescent material is available in bags of various volumes that is ideal for stuffing between the ventilation ducting and the roof or wall, since it allows thermal movement without being dislodged. However, it should be held in place, top and bottom, by plates fixed to the concrete to prevent it being dis- lodged by any pressure pulses in the cell. Foams are available to use for sealing pipe and cable ducts, but in all cases “listing and approval for use and compliance” should be sought from local fire authorities and facility insurers before particular products are used.
Plastic “soil pipes” cast into the floor are a convenient way of carrying cables between test cell and control room. Several such pipes need to be dedicated to cables of the same type to avoid crosstalk and signal corruption. These ducts should be laid to fall slightly in the direction of the cell to prevent liquid flow into the control room and should have a raised lip of 20 mm or more to prevent drainage of liquid into them but positioned so as not to create a trip hazard.
Spare cables should be laid during installation. These pipes can be “capped” by foam or filled with dried casting sand to create a noise, fire, and vapor barrier.
Large power cables may enter a cell through cast concrete trenches cast under the wall and filled with dense dry sand below a floor plate; this method gives both good sound insulation and a fire barrier, and it is relatively easy to add cables later.
Fire and Gas Detection and Alarm Systems for Test Facilities There are three separate system design subjects:
l The prevention of explosion and fire through the detection of flammable, explosive, or dangerous gases in the cell and the associated remedial actions and alarms.
l The suppression of fireand the associated systematic actions and alarms.
l Detection of gasesinjurious to health.
An engine test cell’s gas detection system, supplied by a specialist subcon- tractor, will be fitted to transducers designed to detect various levels of Chapter | 4 Powertrain Test Facility Design and Construction 83
hydrocarbon vapor (see ATEX regulations). In facilities testing fuel cells hydrogen detectors should be fitted in the roof spaces.
Depending on the requirements of the risk analysis valid for the facility, some areas within and outside the cell may be fitted with carbon monoxide sensors. This is particularly important if pressurized and undiluted engine exhaust ducting is routed through a building space, a design feature to be avoided if possible.
Gas detection systems must be linked to the cell control system and, where it exists, the building management system (BMS) in conformity to local and national regulations.
The gas hazard alarm and fire extinguishing systems are always entirely independent of, and hierarchal to, the test cell’s emergency stop circuit system.
The operation of both systems, which can vary significantly, should be specified within the control and safety interlock matrix covered in Chapter 5.
There is much legislation relevant to industrial fire precautions and a number of British Standards. In the UK the Health and Safety Executive, acting through the Factory Inspectorate, is responsible for regulating such matters as fuel storage arrangements, and should be consulted, as should the local fire authority.
The choice of audible alarms and their use requires careful thought when designing the facility safety matrix.
Audible alarms, separate from those visual alarm displays that are a func- tion of the test controller, are usually reserved to warn of fire. The fire alarms usually use electronic solid-state sounders with multi-tone output, normally in the range of 800–1000 Hz, or can be small sirens operating in the range of 1200–1700 Hz. Regulations require that they output a sound level 5 decibels above ambient; since ambient even in the control area may be 80 decibels, most fire alarms fitted into engine test cell areas tend to be painfully loud and thus successful in quickly driving humans out of their immediate area.
However, it is not uncommon for hot, sometimes incandescent, engine parts to trigger false fire alarms through in-cell detectors, so it is most important that the operator is trained and able to identify and kill such false alarm states and avoid consequential automatic shutdown of unassociated plant, or inappro- priate release of a fire suppression system.
Fire Extinguishing Systems
Whatever the type of fire suppression systems fitted in test cells, it is absolutely vital that all responsible staff are formally trained and certified in its correct operation and that this training is kept up to date with changes in best practice and the nature of the units under test.
In the period between the second and third editions of this book, some gas- based fire suppressant systems were banned for use in new building systems since they were judged injurious to the environment.
Table 4.3lists the common fire suppression technologies and summarizes their characteristics, which are covered in more detail in the following paragraphs.
Microfog Water Systems
Microfog or high-pressure mist systems, unlike other water-based fire extin- guishing systems, have the great advantage that they remove heat from the fire source and its surroundings and thus reduce the risk of reignition when it is switched off. The system is physically the smallest available and therefore makes its integration within the crowded service space much easier than the gas-based systems.
Microfog systems use very small quantities of water and discharge it as a very fine spray. They are particularly efficient in large cells, such as vehicle anechoic chambers, where they can be targeted at the fire source, which is likely to be of small dimensions relative to the size of the cell.
Other advantages of these high-pressure mist systems is that they tend to entrain the black smoke particles that are a feature of engine cell fires and prevent, or considerably reduce, the need for a major cleanup of ceiling and walls. Such systems are used in facilities containing computers and high- powered electrical drive cabinets with proven minimum damage after activa- tion and enabling a prompt restart.
Carbon Dioxide (CO2)
CO2was used extensively in the industry until the environmental impact was widely understood. While it can be used against flammable liquid fires it is hazardous to life in confined spaces; breathing difficulties become apparent above a concentration of 4% and a concentration of 10% can lead to uncon- sciousness or, after prolonged exposure, to death. Therefore, a warning alarm period must be given before activation to ensure pre-evacuation of the cell.
CO2is about 1.5 times denser than air and it will tend to settle at ground level in enclosed spaces. The discharge of a CO2flood system is likely to be violent and frightening to those in the region and the pressure pulse will blow out any incompetent blockage of holes made in the cell walls for the transit of cables, etc. The sudden drop of cell temperature causes dense misting of the atmosphere to take place, obscuring any remaining vision through cell windows.
Dry Powder
Powders are discharged from hand-held devices and are designed for high- speed extinguishing of highly flammable liquids such as petrol, oils, paints, and alcohol; they can also be used on electrical or engine fires. It must be remembered that dry chemical powder does not cool nor does it have a lasting smothering effect and therefore care must be taken against reignition.
Chapter | 4 Powertrain Test Facility Design and Construction 85
TABLE 4.3 Characteristics of Major Fire Suppression Systems
Water Sprinkler Inert Gas (CO2) Chemical Gases High-Pressure Water Mist
Cooling effect on fire source Some None None Considerable
Effect on personnel in cell Wetting Hazardous/fatal Minor health hazards None Effect on environment High volume of
polluted water
Greenhouse and ozone layer depleting
Greenhouse and ozone layer depleting
None
Damage by extinguishing agent
Water damage None Possible corrosive/hazardous
by-products
Negligible
Warning alarm time before activation
None required Essential Essential None required
Effect on electrical equipment
Extensive Small Possible corrosive by-products Small
Oxygen displacement None In entire
cell space
In entire cell space At fire source
EngineTesting
Halons
Following the Montreal Protocol in 1987, halons (halogenated hydrocarbons) including Halons 1211, 1301, and 2402 were subject to a slow phase-out down to zero by 2010. These contain chlorine or bromine, thought to be damaging to the ozone layer, and their production has been banned. Existing stocks of Halons 1211 and 1301, both hitherto used for total flooding and in portable extinguishers for dealing with flammable liquid fires, should, by the publication date of this book, have been used up and replacement systems installed.
Inergen
Inergen is the trade name for the extinguishing gas mixture of composition 52%
nitrogen, 40% argon, 8% carbon dioxide. It works by replacing the air in the space into which it is discharged and taking the oxygen level down to<15%
when combustion is not sustained.
There are other alternative fire suppressants of the same type as Inergen, including pure argon, many of which may be used in automatic mode even when the compartment is occupied, provided the oxygen concentration does not fall below 10% and the space can be quickly evacuated.
With all gaseous systems, precautions should be taken to ensure that accidental or malicious activation is not possible. In particular, with carbon dioxide systems, automatic mode should only be used when the space is unoccupied and in conjunction with alarms that precede discharge.
Total flood systems, of whatever kind, are usable only after the area has been sealed. They must be interlocked with the doors and special warning signs must be provided.
Foam
Foam extinguishers could be used on engine fires but they are more suited to flammable liquid spill fires or fires in containers of flammable liquid. If foam is applied to the surface or subsurface of a flammable liquid it will form a protective layer. Some powders can also be used to provide rapid knock-down of the flame. Care must be taken, however, since some powders and foams are incompatible.