Category Archives: FIre Investigation Science

DISTINGUISHING BETWEEN ARCING AND MELTING DAMAGE IN ELECTRICAL RECEPTACLES

Matthew Benfer and Daniel Gottuk
Hughes Associates Inc., USA

Presented at International Symposium on Fire Investigation, 2014

ABSTRACT

The majority of fire-investigation related literature on electrical arcing focuses on copper wiring, both stranded and solid, with some attention paid to steel (i.e., conduit), and relatively little mention of brass. This is despite the relatively equal presence of copper, steel, and brass in receptacles and similar electrical devices. Changes to NFPA 921 in the 2014 edition of the guide expand upon the characteristic traits which can be used to assess whether arcing or melting is present in a conductor. However, most of the characteristic traits of arcing and melting are qualitative and not well defined in NFPA 921, which leads to more subjective evaluations. In addition, a myopic examination of evidence with respect to the presence of one or two characteristic traits can lead to a false indication of arcing. In cases such as this, other evidence of melting (i.e., in close proximity to the area in question) could preclude confirmation of arcing.

The purpose of this work was to determine which characteristic traits are effective in assessing potential arcing damage on receptacle components and wiring. A total of 86 receptacles were evaluated in this study. Thirty-nine receptacles failed as a result of an overheating connection resulting in arcing damage; this included 95 individual conductors. Forty-seven receptacles with fire-induced arcing were also evaluated; this included 87 individual conductors. All of the evaluated receptacles with fire-induced arcing were energized or energized with a load during testing. In contrast, thirty-seven non-energized receptacles with fire induced melting were evaluated with 57 individual conductors.

The characteristic arcing traits which were evaluated include: corresponding damage on the opposing conductor; localized point of contact with a sharp line of demarcation between undamaged and damaged areas; round, smooth shape; resolidification waves; tooling marks visible outside the area of damage; internal porosity; spatter deposits; and small beads and divots over a limited area. The characteristic traits of melting which were evaluated include: visible effects of gravity; gradual necking of the conductor; and pitting, thinning, and presence of holes in the conductor. These traits were taken from the literature (e.g., NFPA 921) and from observations made during the forensic examinations of receptacles and wiring conducted as part of this work. For each characteristic, there were three possible outcomes: Yes, No, and Possible. Yes indicated that the characteristic was judged to be present on the particular conductor; no indicated that the characteristic was judged not to be present on the conductor. Possible indicated that confirmation could not be made either for or against the presence of the characteristic. All of the evaluations were conducted by the same person.

Corresponding damage on the opposing conductor, localized damage with a sharp line of demarcation, and tooling marks outside of the area of damage were observed on significant portions of arc damaged conductors and small numbers of conductors with melting damage; these characteristics were found to be strong indicators of arcing.

Using multiple characteristic traits and contextual information for determination of arcing vs. fire-melting provides greater confidence in the evaluation of damage. In addition, visual examinations were found to be reliable indicators of both arcing and fire-melting for most conductors. However, there are some cases which would benefit from more advanced examination techniques including SEM/EDS examinations, X-ray, CT scanning (X-ray computed tomography), cross-sectioning and polishing, or other metallurgical methods.

Download the complete paper here.

More than 1,000 people taking a pleasure trip on New York City’s East River are drowned or burned to death when a fire sweeps through the boat. The General Slocum disaster was the New York area’s worst disaster in terms of loss of life until the September 11, 2001 attacks. It is the worst maritime disaster in the city’s history, and the second worst maritime disaster on United States waterways.

The riverboat-style steamer General Slocum was built in 1890 and used mostly as a vehicle for taking large groups on day outings. On June 15, the St. Mark’s German Lutheran Church assembled a group of 1,360 people, mostly children and teachers, for their annual Sunday School picnic. The picnic was to take place at Locust Point in the Bronx after a cruise up the East River on the General Slocum.

At about 9 a.m., the dangerously overcrowded boat left its dock in Manhattan with Captain William Van Schaik in charge. As the boat passed 83rd Street, accounts indicate that a child spotted a fire in a storeroom and reported it to Captain Van Schaik. Reportedly the captain responded, “Shut up and mind your own business.” But as the smoke became more obvious, crew members were sent to investigate. By this time, the storeroom, filled with a combination of oil and excelsior (wood shavings used for packing), was blazing out of control. The onboard fire hose, which had never been used, tested or inspected, did not work.

Captain Van Schaik made a fateful decision at this time. Instead of directing the boat to the nearest dock where firefighters could engage the fire, he pointed the boat toward a small island in the East River. He later told investigators that he did not want to risk spreading the fire to the dock and the rest of the city, but the strategy proved deadly for the passengers. Instead of grounding the boat on the sand, the boat crashed onto the rocks of the island’s shore.

At this point, other factors also combined to exacerbate the situation. The lifeboats were so firmly tied to the steamer that they could not be released. The life preservers had not been filled with cork, but a non-buoyant material that made them weighty. The children who used them sank to the bottom of the river. Other children were trampled to death in the panic. More people were killed when the raging fire collapsed some of the decks, plunging them into the fire.

In all, 630 bodies were recovered and another 401 were missing and presumed dead. A cannon was brought to the scene and fired over the river the next day to loosen bodies from the river mud. The boat’s crew, and officers in the Knickerbocker Company, owner and operator of the General Slocum, were charged with criminal negligence. However, only Captain Van Schaik received a prison sentence. He was supposed to serve 10 years, but was pardoned due to old age in 1908. President Theodore Roosevelt fired the chief inspector of the U. S. Steamboat Inspection Service in the aftermath of the accident; wholesale changes in the industry followed. A mass grave was set up in Queens for the victims and a yearly memorial was held to honor their memory.

Source: History.com
Image: The Library of Congress – shows the mass of burned timbers and ruined metal, showing broken paddle wheels shaft.

On this day in 1937, the German airship Hindenburg, the largest dirigible ever built, explodes as it arrives in Lakehurst, New Jersey. Thirty-six people died in the fiery accident that has since become iconic, in part because of the live radio broadcast of the disaster.

The dirigible was built to be the fastest, largest and most luxurious flying vessel of its time. It was more than 800 feet long, had a range of 8,000 miles, could carry 97 passengers and had a state-of-the-art Mercedes-Benz engine. It was filled with 7 million cubic feet of hydrogen, even though helium was known to be far safer, because it made the flying ship more maneuverable.

The Hindenburg had made 10 successful ocean crossings the year before and was held up by Germany’s Nazi government as a symbol of national pride. Flying at a speed of 85 miles per hour, the Hindenburg was scheduled to arrive in New Jersey at 5 a.m. on May 6. However, weather conditions pushed the arrival back to the late afternoon and then rain further delayed the docking at Lakehurst. When the dirigible was finally cleared to dock, Captain Max Pruss brought the ship in too fast and had to order a reverse engine thrust. At 7:20 p.m., a gas leak was noticed. Within minutes, the tail blew up, sending flames hundreds of feet in the air and as far down as the ground below.

A chain reaction caused the entire vessel to burn instantly. The nearly 1,000 spectators awaiting the Hindenburg‘s arrival felt the heat from a mile away. Some on the blimp attempted to jump for the landing cables at the docking station but most died when they missed. Others waited to jump until the blimp was closer to the ground as it fell. Those who were not critically injured from burns often suffered broken bones from the jump. Fifty-six people managed to survive.

On WLS radio, announcer Herbert Morrison gave an unforgettably harrowing live account of the disaster, “Oh, oh, oh. It’s burst into flames. Get out of the way, please . . . this is terrible . . . it’s burning, bursting into flames, and is falling . . . Oh! This is one of the worst . . . it’s a terrific sight . . .oh, the humanity.”

Source: History.com

ALUMINUM PHOSPHIDE-BASED FUMIGANTS AS AN IGNITION SOURCE IN AGRICULTURAL COMMODITY STORAGE STRUCTURE FIRES

John L. Schumacher, MChE, PE, CFI, CFPS
Zachary J. Jason, PE, CFEI
Advanced Engineering Investigations Corporation, USA

Presented at International Symposium on Fire Investigation, 2012

ABSTRACT

Raw agricultural commodities, such as corn, soybean, rice and wheat, are typically stored in bins and silos prior to shipment. During storage, it is often necessary to protect the commodities from damage by insects and pests. A common protection method utilized is the addition of solid fumigant pellets or tablets to the commodity.

One of the most common solid fumigants employed is a blend of aluminum phosphide, ammonium carbamate and other inert ingredients. Aluminum phosphide reacts with atmospheric water and moisture in the commodity based on the following equation:

AlP + 3H2O = Al(OH)3 + PH3 + Heat

The reaction yields phosphine gas (PH3), which is highly toxic to insects, pests and humans. The reaction is exothermic, which means heat is generated alongside the other products. Phosphine gas has a lower flammable limit (LFL) of about 1.8% gas in air and can ignite spontaneously at concentrations above the LFL. The ammonium carbamate is added to the mixture to reduce the potential fire hazard by generating ammonia and carbon dioxide, which act as inerting gases. The carbon dioxide reduces the tendency of phosphine to auto-ignite in air. The decomposition reaction is as follows:

NH2COONH4 = 2NH3 + CO2

Improper application of the fumigant tablets or pellets can lead to fires. This paper provides basic product information, and discusses the chemistry, application methods, previous testing, and ignition scenarios associated with solid fumigants containing aluminum phosphide. A case study of a fire that occurred in a metal grain bin containing wheat will be presented.

Presented at International Symposium on Fire Investigation, 2012

On April 27 in 1865, an explosion on a Mississippi River steamboat kills an estimated 1,547 people, mostly Union soldiers returning home after the Civil War. Although this disaster near Memphis took a huge toll, it was barely noticed against the backdrop of the end of the Civil War, a conflict in which tens of thousands had died.

The previous day had marked the final surrender and end of armed resistance by the remaining Confederate forces. Only two weeks earlier, President Abraham Lincoln had been assassinated. Prisoners of war who had been held in hellish conditions in Alabama’s Andersonville and Cahaba prison camps were trying to make their way home to Illinois. The steamboat Sultana was one of their only options.

At 2 a.m. on April 26, the steamboat left Vicksburg, Mississippi. It was built to hold 376 passengers, but reports say that there were as many as 2,700 people on board as it lumbered slowly up the Mississippi River. It took 17 hours to make the journey to Memphis, where it stopped to pick up more coal.

A couple of hours past midnight, the trip came to a sudden end: near the Arkansas side of the river, one of the Sultana’s three boilers suddenly exploded. Hot metal debris ripped through the vessel and two other boilers exploded within minutes of the first. The passengers were killed by flying metal, scalding water, collapsing decks and the roaring fire that broke out on board. Some drowned as they were thrown into the water, but rescue boats were immediately dispatched, saving hundreds of lives.

The final tally of casualties was hotly disputed. Some believe it may have been almost 2,000 people, though the U.S. Army said that only 1,200 people had been killed. Local customs officials determined that 1,547 were killed; that became the generally accepted count. The Sultana disaster remains one the most deadly maritime accidents in U.S. history.

Source: History.com
Image: Library of Congress

The cargo ship Fort Stikine explodes in a berth in the docks of Bombay, India, killing 1,300 people and injuring another 3,000 on April 14 in 1944. As it occurred during World War II, some initially claimed that the massive explosion was caused by Japanese sabotage; in fact, it was a tragic accident.

The Fort Stikine was a Canadian-built steamship weighing 8,000 tons. It left Birkenhead, England, on February 24 and stopped in Karachi, Pakistan, before docking at Bombay. The ship was carrying hundreds of cotton bales, gold bullion and, most notably, 300 tons of trinitrotoluene, better known as TNT or dynamite. Inexplicably, the cotton was stored one level below the dynamite, despite the well-known fact that cotton bales were prone to combustion.

In the middle of loading, smoke was seen coming from the cotton bales and firefighters were sent to investigate. However, emergency measures, such as flooding that part of the ship, were not taken. Instead, about 60 firefighters tried to put out the fire with hoses throughout the afternoon. Unfortunately, the TNT was not unloaded during the firefighting efforts.

Eventually, the firefighters were ordered off the ship but kept dousing the fire from the docks. Their efforts were in vain; the TNT was ignited, and at 4:07 p.m., the resulting explosion rocked the bay area. The force of the blast actually lifted a nearby 4,000-ton ship from the bay onto land. Windows a mile away were shattered. A 28-pound gold bar from the Fort Stikine, worth many thousands of dollars, was found a mile away. Everyone in close vicinity of the ship was killed.

Twelve other ships at the docks were destroyed and many more were seriously damaged. Fires broke out all over the port, causing further explosions. Military troops were brought in to fight the raging fires and some buildings were demolished to stop it from spreading. The main business center of Bombay was not safe for three days after the explosion.

Source: History.com
Image credit: Library of Congress

In one of the darkest moments of America’s industrial history, the Triangle Shirtwaist Company factory in New York City burns down, killing 145 workers, on March 25, 1911. The tragedy led to the development of a series of laws and regulations that better protected the safety of factory workers.

The Triangle factory, owned by Max Blanck and Isaac Harris, was located in the top three floors of the 10-story Asch Building in downtown Manhattan. It was a sweatshop in every sense of the word: a cramped space lined with work stations and packed with poor immigrant workers, mostly teenaged women who did not speak English. At the time of the fire, there were four elevators with access to the factory floors, but only one was fully operational and it could hold only 12 people at a time. There were two stairways down to the street, but one was locked from the outside to prevent theft by the workers and the other opened inward only. The fire escape, as all would come to see, was shoddily constructed, and could not support the weight of more than a few women at a time.

Blanck and Harris already had a suspicious history of factory fires. The Triangle factory was twice scorched in 1902, while their Diamond Waist Company factory burned twice, in 1907 and in 1910. It seems that Blanck and Harris deliberately torched their workplaces before business hours in order to collect on the large fire-insurance policies they purchased, a not uncommon practice in the early 20th century. While this was not the cause of the 1911 fire, it contributed to the tragedy, as Blanck and Harris refused to install sprinkler systems and take other safety measures in case they needed to burn down their shops again.

Added to this delinquency were Blanck and Harris’ notorious anti-worker policies. Their employees were paid a mere $15 a week, despite working 12 hours a day, every day. When the International Ladies Garment Workers Union led a strike in 1909 demanding higher pay and shorter and more predictable hours, Blanck and Harris’ company was one of the few manufacturers who resisted, hiring police as thugs to imprison the striking women, and paying off politicians to look the other way.

On March 25, a Saturday afternoon, there were 600 workers at the factory when a fire broke out in a rag bin on the eighth floor. The manager turned the fire hose on it, but the hose was rotted and its valve was rusted shut. Panic ensued as the workers fled to every exit. The elevator broke down after only four trips, and women began jumping down the shaft to their deaths. Those who fled down the wrong set of stairs were trapped inside and burned alive. Other women trapped on the eighth floor began jumping out the windows, which created a problem for the firefighters whose hoses were crushed by falling bodies. Also, the firefighters’ ladders stretched only as high as the seventh floor, and their safety nets were not strong enough to catch the women, who were jumping three at a time.

Blanck and Harris were on the building’s top floor with some workers when the fire broke out. They were able to escape by climbing onto the roof and hopping to an adjoining building.

The fire was out within half an hour, but not before 49 workers had been killed by the fire, and another 100 or so were piled up dead in the elevator shaft or on the sidewalk. The workers’ union organized a march on April 5 to protest the conditions that led to the fire; it was attended by 80,000 people.

Though Blanck and Harris were put on trial for manslaughter, they managed to get off scot-free. Still, the massacre for which they were responsible did finally compel the city to enact reform. In addition to the Sullivan-Hoey Fire Prevention Law passed that October, the New York Democratic set took up the cause of the worker and became known as a reform party.

Source: History.com

Mark Goodson PE
Lee Green PE
Michael Shuttlesworth PE
Goodson Engineering
Denton, Texas USA

Presented at International Symposium on Fire Investigation, 2014

ABSTRACT
One of the difficulties that has faced engineers who examine electrical or mechanical items and / or devices after a fire is that of cleaning the item. The key adage in cleaning is essentially a medical command – primum non nocere, or “do no harm.” The cleaning technique will preferably cause no damage to the artefact being examined. Successful cleaning allows for both microscopic, visual, and SEM / EDX analysis.

In a fire, it is not uncommon for fire artefacts (wires, as an example) to require cleaning. Historical cleaning techniques have relied upon ultrasonic cleaning as a means for debris removal. Ultrasonic cleaning makes use of mechanical (sonic) energy to cause debris to dislodge from artefacts. How successful this technique is depends (in part) upon the energy imparted, the solvent used, and the interface between the wire and the debris. In the case of partially pyrolyzed PVC insulation, there are conditions that occur (depending upon the state or extent of pyrolysis) where no amount of mechanical agitation will remove the fire debris.

Oxides can be removed from wires by the use of surfactants or cleaners, some of which can have an etching effect on the metal. Treatments such as Alconox  or Simple Green  sometimes work sufficiently, while a more aggressive oxide remover (Branson OR)  relies on citric acid to help clean the wires. With more aggressive reagents, the user runs the risk of etching the metal and ruining the surface finish.

The writers describe a technique for removing fire debris from metal objects (wire, CSST) for use in removing fire debris. The technique is referred to as plasma ashing . In plasma ashing, a vacuum is created around the artefact, and a carrier gas is introduced (such as O2). An RF field (13.56 MHz) is applied, and the oxygen takes on a monatomic state. Essentially, a plasma i s created, and the monatomic O is free to react with organics associated with the fire debris. This process is also referred to as a glow discharge . The end result is that organics are removed from the artefact, and the ashing takes place at low temperatures – sufficiently low such that grain structure of the metal is not changed. This technique is essentially what is used in one of the manufacturing steps for making integrated circuits (ICs). As such, it imparts sufficiently low energy such that crystalline semiconductor structures are not damaged.

We compare and contrast plasma ashing with other modalities of cleaning. More particularly, we note (through visual microscopy) the efficacy of ashing and ultrasonic cleaning, as well as material removal rates. We show that despite its relative expensive capital costs, ashing represents a cleaning technique that does what other modalities fail to do – consistent removal of organic debris with no damage to the underlying substrate.

Download the complete paper here