Fires, explosions, chemical releases, reactions and other similar catastrophic occurrences are all part of life in today’s complex industrial society. We wish these things didn’t happen but they do. We take all possible precautions in the construction of our facilities and in the handling of dangerous materials yet the old cook’s adage is still true. You do “have to break eggs if you want to make an omelet.” Incidents will occur and responses will be necessary.
The amount of property damage and the number of injuries or fatalities is usually a factor of the response time for those responsible for the mitigation and control of the incident. The sooner a response team gets on the scene the less property will be damaged and the smaller the number of fatalities. Because of prompt medical attention those with injuries will have a better chance of survival and a more complete recovery.
Unfortunately, emergency dispatchers are not clairvoyant; they cannot dispatch a response team to an incident they do not have knowledge of. We frequently hear of instances in which a passer-by noticed smoke or smelled a strange odor and called 911. All too often this is “too little too late” and the home and other property is destroyed or damaged beyond repair and the occupants are overcome. All this might have been prevented, or at least mitigated, by a ten dollar smoke detector if the property owner had taken the trouble to obtain and install one.
We have all heard campaign after campaign by fire departments trying to get home owners to install these alarms and most importantly to maintain them on a regular basis yet, far too many homes and businesses remain unprotected by these simple and inexpensive devices.
The same principle applies to larger, more destructive incidents within industrial complexes. All fires start small, they may not stay that way very long but they do start small and the sooner we know about them the more likely we are to be able to extinguish them without injuries or significant damage to the facility.
All this did not come about by accident, neither did it happen overnight. It is rather, an evolutionary progression that began in ancient times when man began to take fire into his dwellings to cook his food, keep him warm and give him light in the darkness. As man moved from caves into constructed dwellings and to consolidate these into villages, the need to combat fires became ever more important, giving rise to the fire patrols found in ancient Rome and other cities.
Unfortunately, even the most sophisticated detection and alarm systems have one inherent drawback: no alarm is of any value if no one is around to hear it and respond appropriately. Hence the large expenditures for monitoring services. This issue has been around since the time of the Roman Empire when officers patrolled the streets ready to raise the alarm upon discovery of a fire.
This protocol for initiating response to an “alarm of fire” endured throughout colonial America and in a much more sophisticated format endures to the present day in the form of monitoring services provided by various security companies.
One of the earliest “security systems” employed in colonial America was the placement of a barrel of water sitting on top of a charge of gunpowder in the rafters or attic of a building. In the event of fire the gunpowder was supposed to ignite, explode and blow up the barrel, scattering the water on the fire; hopefully extinguishing it.
The noise of the explosion would also serve to rouse the neighborhood so that an additional response could be mounted. The trick was to size the powder charge so as to blow the barrel apart and disperse the water without taking down the building along with it. Crude and primitive though it was, this system seems to have been deployed and to have actually worked on occasion.
A modern version of this technique is the carbon tetrachloride (CCl4) “Bomb.” This was a thin-walled sealed glass vessel containing carbon tetrachloride which was hung on the wall or suspended from the ceiling of the structure to be protected. In the event of a fire, the carbon tetrachloride, which is a very volatile substance, would burst the container and release the contents which would subsequently vaporize and extinguish the fire. These appliances worked fairly well and were in use until about the end of WWII. They are still occasionally encountered in older buildings.
Their main drawback was that carbon tetrachloride (often marketed as “Pyrene” and Halon 104) reacts with heated metal to produce phosgene (COCl2) which is lethal and saw service as a war gas in WWI. In spite of its lethal potential, carbon tetrachloride continued to be employed as a common fire extinguishing agent until about the end of WWII. This was mainly due to the fact that the material will not conduct electricity and was therefore considered safe to use on electrical fires particularly those in vehicles and aircraft.
With the advent of the electric telegraph in the last half of the nineteenth century the ability to monitor numerous locations from a central office became reality. Fire alarm boxes, such as those made by the Gamewell company, began to dot the landscape in major cities and the telephone expedited fire reporting in more rural areas until supplanted by the radio.
Fires are not the only types of incidents that need to be promptly detected and reported. Hazardous and/or toxic environments can also pose a threat to life and property. As the world transitioned from an agrarian to an industrial society and the steam engine supplanted animal power, coal largely replaced wood as the primary source of energy for the emerging “Industrial Revolution.”
Wood was cut, or gathered, in open forests while coal was obtained from underground mines. As these mine shafts were extended deeper the need for ventilation, both to provide adequate oxygen and to disperse flammable and toxic gases became apparent. Early on, miners discovered that a canary taken into the mine would stop singing when the atmosphere became oxygen deficient or toxic. Since a bird's metabolism rate is higher than that of a human, the effects of exposure to a hazardous atmosphere would be noticeable in time for the miners to escape before the contamination reached a lethal concentration.
This technique undoubtedly saved many lives but it had one glaring shortcoming. It told the miners that the atmosphere was becoming hazardous but it did not identify the hazard. Was it toxic or was it flammable (or both)? Methane (CH4) is commonly present in coal mine workings. If the concentration of methane reaches the lower explosive limit (LEL) of five percent (five percent methane and 95 percent). The open flame cap lights used by the miners will assure ignition and guarantee an explosion.
To detect flammable atmospheres, Sir Humphry Davy, in 1815, developed the Davy Safety Lamp, the first mechanical hazardous atmosphere monitor. This appliance, which continues to be approved for use to the present day, consists of a small adjustable oil fueled flame surrounded by an enclosure of fine wire gauze within a glass chimney.
In use, the flame height is adjusted so that the flame lies between two witness marks etched on the glass globe. If the lamp encounters a flammable atmosphere the flame becomes taller and more luminous. If the atmosphere is deficient in oxygen or has a gas content above the Upper Explosive Limit (UEL) and is therefore too “rich” to burn the flame will turn yellow and emit black smoke.
Should the atmosphere be completely void of oxygen (as in an inerted tank, for example) the flame will go out. An experienced lamp operator can often provide clues as to the nature of the atmospheric contaminates from the color and nature of the flame.
The advent of electricity and the Wheatstone bridge in the later part of the nineteenth century ushered in the electrical version of the Davy lamp. This instrument relies on the fact that the amount of electrical resistance in a wire filament varies with the temperature of the wire. In the flammable gas detector the filament is very similar to those encountered in ordinary incandescent flashlight bulbs and is surrounded by a fine wire gauze as we saw enclosing the flame in the Davy lamp.
This filament is part of a Wheatstone bridge which is balanced or “zeroed” in an uncontaminated atmosphere. The filament is heated by the current that is used to operate the bridge. As the instrument encounters a flammable component of the atmosphere, combustion takes place on the surface of the filament causing the temperature to rise and the Wheatstone bridge to become unbalanced, thus causing a current to be detected by the galvanometer connected across the bridge. The amount of this current is proportional to the concentration of the flammable component of the atmosphere. Note that this instrument (now discontinued by the manufacturer but with a great many still in service) is electrical but not “electronic.”
These instruments are noted for being rugged and reliable but they did have limitations: the filament was subject to “poisoning” by heavy metals, most commonly the tetraethyl lead formerly used as an “anti-knock” agent in gasoline.
As the “Golden age of Chemistry” matured, propelled in large part by the advent of the automobile with its voracious appetite for gasoline and the genesis of synthetic materials (“plastics”) which engendered the ”petrochemical industry,” so called “hazardous materials” became increasingly visible as articles of commerce.
As this “visibility” increased, so did the chance for incidents during treansportation thus, the need for municipal fire departments to respond to incidents involving “en-route” shipments which may consist of any one of a myriad of commodities with which the personnel of the individual response organization may or may not be familiar. This is not what we might wish for but it is reality; at least until more specialized agencies such as manufacturer’s or shipper’s response teams can arrive to relieve these “blindsided” responders who desperately need the answer to the questions “What,” “Where,” and “How Much.”
As technology has adanced, electronic (perhaps “electro-chemical” would be a be a better term) instrumentation has largely replaced “wet” chemistry for on-site analysis. This innovation has reduced both the cost and the time required to obtain essential data. This has been most helpful but, it is also expensive in the case of the infrequent user, and the initial cost of many instruments is far beyond the means of many small volunteer departments.
However, this does not mean that these departments are without resources when faced with a situation involving a rarely encountered commodity. For example, A strip of absorbant paper dampend with an aqueous solution of Lead Acetate (Pb(C2H3O2)2) and suspended in a suspected manhole will still turn black in the presencce of Hydrogen Sulfide (H2S) as it did before the advent of the electrochemical monitoring electrode.
An extract of red cabbage will go through the entire spectrum of colors from red to blue in response to the existing pH (blue being indicative of a strong base and red denoting a strong acid) as it did before the advent of pH hydrion paper. This extract can be homemade or purchased by the gallon and is very convenient for tracing spilled material or judging the efectiveness of nutralization. It can also be prepared as needed, Any grocery store will have red cabbage.
This brings to mind another problem encountered with many electro-chemical monitoring instruments: The sensory electrodes have a very definite, and in some cases a very short, shelf life. This is particularly true in the case of equipment stored or used in very dry locations such as the desert southwest, where I reside. This makes it difficult for those ocassional responders who need such instrumentation very rarely. These devices commonly consist of a cup containing a chemical paste which is in contact with electrodes which, in turn are connected to a box enclosing the electronics. If and when this paste dries out the electrode becomes useless.
The solution to this problem often lies in the selection of instruments, such as the flame ionization detector or explosimeter which have a long (in many cases indefinite) shelf life. In most cases, these instruments will not be as specific as those using the cup electrode but they trade specificity for longevity and broader coverage and it behoves those charged with instrument selection to consider what we really want (need) to know. If we are responding to spill of unleaded gasoline do we need a portable chromatogaph or will a simple explosoimeter suffice? We know “what” all we need is “where”and “how much” (the concentration, are we near the LEL or above the UEL? Can a responder enter the area wearing protective clothing and SCBA?)
In many cases an expierenced operator can give us all we need to know in order to determine the best and safest course of immediate action. That is all we really need at the moment. More refined analysis can await the arrival of more sofisticated instrumentation as well as qualified and experienced personnel to operate it.
Modern instrumentation has contributed much to the safety and success of emergency response operations in general and to Haz Mat incidents in particular. It has made possible the safe consumption of many of the modern day materials and products that we now take for granted but were unknown to our parents’ generation. Hydrogen Floluride (“anhydrous Hydroflouric Acid”, HF) is but one example.
Known only as an etching agent for small glass items and a laboratory curiosoty when I was a student, HF was thought to be too corrosive and too dangerous for any practical purpose. The introduction of lead free gasoline created a need for this comodity in tank car quanties and immediately protocols to ensure its safe transportation and utilization were promulgated and implemented. Today, this commodity is a common article of commerce.
Instrumentation is not a “dead” or completed field. As new materials and formulations enter the market place and arrive in the transportation network, new detection protocols will perforce be required to deal with them safely and in a timely manner. New Techniques, and newly developed instruments to utilize them, along with better operator training allows these commodities to be integrated into general commerce by industry and transported to consumer markets safely and efficiently.