MANHOLES AND THEIR HAZARD POTENTIAL

MANHOLES AND THEIR HAZARD POTENTIAL

Manholes serve various functions. Industry, utilities, and public authorities use manholes in providing communities with facilities for services such as gas, electricity, telephones, sewers, public transportation, traffic (lights) control, and cable television. Some manholes serve more than one purpose.

Manholes can present many hazards for responders and civilians, especially in metropolitan areas, where they are abundant and located in populated sections. They are not limited to city streets but also can be found on sidewalks, in gutters, beside buildings, in commercial and residential areas, in places of entertainment, and even in playgrounds and other complexes where large numbers of people congregate.

In use since before the turn of the century, many systems housed by manholes are old, and the wires under the street are hard to reach. This applies especially to utility systems, since it was not economically feasible to replace and redesign the older systems as the demands for electricity and gas increased.

The recent increased concern about the environment has focused authorities’ attention on manholes, however, and the Environmental Protection Agency has mandated that manhole systems be brought up to code nationally. The EPA, for example, now forbids the use of asbestos as a wire covering and has directed that any asbestos present in old systems be removed. PCB-containing oils used to insulate and cool transformers also are being replaced with products that are less threatening to health and the environment.

Other environmental and physical dangers presented by manholes include the presence of carbon monoxide or other gases that in high concentrations could displace oxygen within the tunnels, PVC in wire insulation, PCBs in transformers, high-vapor pressures, and the possibility of explosions.

The uses of manholes and the hazards they present may be varied, but these systems also have some characteristics in common.

SEWER MANHOLES

From the perspective of contents, incidents involving sewer manholes present fewer dangers for responders than other types of manholes. Usually found in the middle of the street (as opposed to the gutter area or sidewalk), the newer manholes generally arc numbered and marked “W & S” or “SEWER.” The potential for greatest danger with regard to sewer manholes is the pooling of marsh gas (see sidebar on page 58) and the presence of combustibles in the hole. Fires (from the perspective of typical, independent incidents—not the worstcase scenario) in this type of manhole are considered “Class A” and can be extinguished with water.

TRANSPORTATION MANHOLES

Usually found in cities that have subways or other underground transportation systems, transportation manholes pose one of the greatest dangers for firefighters. These holes always contain high-voltage electricity and sometimes are located in inaccessible locations such as under subway tunnel tracks, where they are subject to the marsh gas that seeps in from the ground below. The combustibles present in these manholes magnify the potential for problems.

The shapes and sizes of transportation manholes are determined by their uses. Some contain huge transformers. In Boston, these manholes are marked “MBTA,” to denote the Massachusetts Bay Transportation Authority. Carbon dioxide extinguishers and/or dry chemicals are effective for fires in these locations.

GAS MANHOLES

Similar to transportation manholes, gas manholes present danger/explosion potential. Heavy metal sewer covers can explode up to 100 feet into the air, and their location near gutters or on sidewalks poses a risk to passersby as well. Gas holes contain low(household use), intermediatecommercial), or high-pressure (main line) lines. Some gas manholes are very small and are used as shutoffs, while others are quite large and can contain a number of lines of varying pressures. Gas manholes may be marked with the city’s name (“BOST GAS” for Boston Gas) or just “GAS.” the age of the holes may make the letters on the covers illegible. Fighting fires in gas manholes usually is limited to shutting off the gas and then treating the contents as Class A.

TELEPHONE MANHOLES

Telephone manholes incorporate a certain amount of electricity. They also may accommodate other utilities’ wires, changing the character of the fire. The main danger posed by telephone manholes is that they usually are close to other types of manholes where gas, conductivity, and burning combustible insulation can be problems. These manholes are marked with the name or symbol of the local telephone company.

ELECTRICITY MANHOLES

Electricity manholes are the most dangerous. They encompass several types of the dangers inherent in manhole incidents in general, are subject to marsh gas, and may be used to carry other utility lines. Their greatest hazards, of course, are the enormous amount of electricity present—-sometimes as much as 345,000 volts—and the PCBs that commonly are found in oil used to insulate and cool the transformers. Experience has shown that killing the power in these manholes is difficult and time-consuming. Electricity manholes usually are designated with the name or a shorter derivative of the name of the local electric company. Numbers appearing on the rim of the hole also may help to identify the manhole that presents the most serious hazard. Fires in electricity manholes may be treated as Class A fires after the power has been shut off, of course; otherwise, they are considered Class C fires and must be extinguished with carbon dioxide and/or dry chemical. (The worst possible scenario would constitute a hazardous-materials incident.)

(Photos by authors.)

Emergencies involving underground wires and manholes call for a familiarity with the underground setup as well as a knowledge of the potential problems associated with the various wires and gases that may be present. The cooperation of the fire department and the utility companies—including prompt response to all emergencies—as well as interagency preplanning are essential to the successful mitigation of a fire in this type of manhole.

LESSONS LEARNED FROM EXPERIENCE

The following scenario illustrates some of the problems responders face in incidents involving manholes. A huge manhole exploded recently in the downtown section of Boston during the early morning hours. By 7:30 a.m., there had been three explosions, one of them causing a square manhole (transformer) cover to shatter and spew cover pieces about 10 feet into the air (covers, as noted before, can go as high as 100 feet in the air). Flames and thick, black smoke poured out of the four-foot by four-foot hole in the street, located two inches from the gutter.

When the fire department arrived, no one knew what was burning underground. The source finally was narrowed down to either the wires, the wooden platform at the bottom of the hole used by workers when repairing the wires, oil from the large transformer within the manhole, or a combination thereof. The transformer also contained an undetermined amount of liquid, estimated by the utility to be anywhere from 100 to 500 gallons.

The guesswork continued to another level. Did the liquid contain PCBs, toxic contaminants that w’ould require special handling and disposal? Was the liquid a silicone (used for insulating and cooling purposes)? Regardless of w’hich substances were present, the smoke and fumes they generated could cause cancer.

The morning rush hour was approaching; hundreds of students were coming out of the subways, while other residents were beginning their morning commutes to school and work. The incident grew to include the need for directing and diverting traffic and managing the flow of curious onlookers and other pedestrians. Public safety was called in to manage these aspects of the emergency. Several patrol cars from surrounding police departments were on scene, as were rescue teams with four men in Tyvex® suits for close proximity work.

Even though the fire had been raging for some time, no one could get close enough to the scene to ascertain its cause because firefighters could not be sent into the hole to extinguish the blaze. The incident commander requested that the electric company shut oft all electricity in the manhole. Voltage was estimated to be between 13,800 and 345,000. No one had an immediate knowledge of the amount because of the frequent changes and additions made to the lines to accommodate new construction and renovation projects. The fire eventually was extinguished with carbon dioxide and water.

We can learn much from this incident:

• Many manholes can contain highvoltage lines and combustible material; consequently, exercise extreme care at all times to prevent injuries.
• Electricity manholes can be totally shut off only by isolating the entire manhole from adjacent holes.
• Transformers in manholes may contain combustible mineral oil as the dielectric coolant. The PCB content of the mineral oil in these transformers generally is not known. So consider it a PCB danger until told otherwise by the utility company. With preplanning you can have this information available at the beginning of the incident. In New York City, for example, utility’ companies must provide the fire department with a list of manholes that have PCB-containing oil in the transformers. This list is carried to incidents by the fire department.
• Consult the utility company before selecting the extinguishing agent.

SOME RESOURCES ON MANHOLES

Additional information on manholes may be found in the following resources:

• NFPA 328, Recommended Practice for the Control of Flammable and Combustible Liquids and Gases in Manholes, Sewers, and Similar Underground Structures.
• American Insurance Association, Fire Prevention Code.
• NFPA 30-1984, Flammable and Combustible Liquids Code.
• NFPA 325M-1984, Fire Hazard Properties of Flammable Liquids. Gases, and Volatile Solids.
• NFPA 329-1987, Recommended Practice for Handling Underground Leakage of Flammable and Combustible Liquids.
• NFPA 495-1985, Code for the Manufacture, Transportation, Storage and Use of Explosive Materials. ■
• Automatically notify the agencies involved when an incident occurs. The proper agency can identify the
• uses of the manhole, any combustible materials in the manhole, and the PCB content of the mineral oil (if present) in the transformers.
• Check all buildings that possibly could be affected by the incident.
• Perhaps most important, you must properly identify the manhole.

Although the delay in the incident discussed above was considerable, the Boston Fire Department district chief correctly questioned whether all the electricity in the manhole had been shut off. Seeing no need for a rescue, the chief officer safely positioned personnel away from the manhole and did not choose extinguishing agents until he fully understood the situation. Safety, accurate identification, and proper use of extinguishing agents were instrumental in the successful and safe mitigation of the incident. Yet considerable damage from the fire itself and the time and cost factors of delayed business openings elevated the toll.

RECOMMENDATIONS

• As noted, not all manholes are the same; nevertheless, the following suggestions can be applied in all incidents involving these systems. On the scene it is important to do the following:

Identify the location and request the user of the manhole (utility company, sewer, or transit authority, etc.) to come on scene to make known the contents of the manhole. Wait until the agency arrives on the scene before taking any drastic actions—unless life is involved.

Perform search and rescue and protect the exposures, but do not initiate any action to extinguish the fire until the company commander has consulted with the utility company if you arrive when a fire is in progress. When in doubt, wait it out.

Notify fire alarm of the conditions and take appropriate action to check the exposures for feedback from the shorted power lines.

Place apparatus and position firefighters to avoid contact with fumes or smoke from the manhole involved. Manhole covers explode violently. Also, should a transformer explode and cause oil containing PCBs to contaminate apparatus and manpower, these resources would have to be placed out of service for decontamination.

If necessary, the officer in charge should consider ordering the utility companies to remove the manhole covers in line with the one involved to relieve pressure buildup. It is dangerous for these covers to be removed by anyone but the proper agency.

Be prepared with special protective equipment (a Level A fully-encapsulating suit) should entering the manhole be necessary. This should he done only if a worker has been trapped, the fire has been extinguished, the electricity’ has been shut off, and the fire chief and the utility concur on this dangerous action.

Establish safety zones. Be especially careful near any manhole that shows signs of being under pressure.

Never turn your back to a manhole.

Always stand by to assist the utility company until it indicates that the services of the fire department are not needed.

Respect manholes; they can be extremely dangerous.

Before the incident, it is important to do the following:

Schedule training sessions with various agencies to gain better understanding of the dangers, contents of manholes, and company or agency operating procedures.

Establish a hot line or at least 24hour communication with every agency.

• Have each agency and utility designate an employee to be the liaison with the fire department.

Manholes dot our cities and towns from end to end and contain an innumerable amount of wires, pipes, conduits, and other equipment and substances, necessitating widespread cooperation between officers and supervisors of responding units and an ever-changing array of agencies, since fire and other threats posed by manholes usually differ from incident to incident.

Formulating charts with regard to immediate response and responsibilities for every type of manhole is virtually impossible. Accordingly, because the fire chief and immediate support staff are the first on the scene, the overriding responsibility for managing and mitigating the emergency rests on them. However, the responsibility entails establishing close cooperation between the fire department and the utility company, seeking and using the utility company’s expertise, and initiating preplanning and training programs. Information and instructions on file must be comprehensive and constantly updated. Given the often dangerous nature of today’s emergencies involving manholes, the role of the firefighter in their mitigation should be scrutinized and reevaluated.