research_mgm_fire_1.docx
The MGM Grand Hotel was a 23 story hotel and casino facility located at the intersection of East Flamingo Road and Las Vegas Boulevard, currently in use as Bally's Casino. The hotel consisted of 21 stories of guest rooms situated above two non-hotel stories- a double main level and casino and an interstitial space used for gaming floor security. The floors were numbered with an alternative numbering system used by the MGM Grand owners, depicted in Fig.1. Immediately adjacent to the casino and performance areas on the first floor to the east were a series of restaurants, clustered in the central portion of the building.
Construction on the building broke ground during 1972 and it was ultimately opened to the public in December of 1973. The building consisted of different construction types of varying efficacy with respect to fire protection. The hotel floors were resistant to fire and utilized a steel framing members which were protected by gypsum wall board (GWB) and reinforced concrete. Partitions were constructed from steel studs and GWB. The casino and interstitial levels were more sparsely protected; in some instances partitions did not fully extend above ceilings, an intention by the HVAC designer (NFPA, 1982). On the morning of Nov. 21, 1980, 85 people died and more than 700 were injured as a result of a fire at the MGM Grand Hotel. This was the second largest life-loss hotel fire in United States history. At approximately 7:00 AM on November 21, an employee of The Deli restaurant (Plan in Fig. 2) first noticed a small fire in the kitchen area while arriving to work. This employee notified hotel security, who in turn notified the fire department. Security began to evacuate the casino floor shortly thereafter, with eyewitnesses also reporting a rapid appearance of smoke. Several guests were trained firefighters and assisted in the evacuation process; they noted that the fire began to superheat the area and penetrate the upper ceiling approximately three to four minutes after evacuation began (NFPA, 1982). It was determined during the investigation that the fire originated in the wall soffit of the side stand in the Deli, one of five restaurants located on the casino level. The investigators concluded that several factors contributed to the cause of the fire but the primary source of ignition was an electrical ground fault. At the time the fire was discovered, the restaurant was not yet opened for business. At approximately 7:05 a.m., a supervisor of a marble and tile setting crew entered the Deli to examine the premises for broken tiles. The employee first observed a reflection of a flickering light and, upon closer inspection, discovered a wall of flame traveling from the countertop to the ceiling. He immediately notified MGM security about the fire and proceeded to secure a hose line and fire extinguisher. The employee repeatedly attempted to contain the fire but - by that time - the heat, smoke and pressure buildup was so intense that he was knocked down each time he tried to enter the Deli. Realizing the gravity of the situation, he decided to leave the area. At the same time, other employees noticed the spreading fire and tried unsuccessfully to extinguish the growing flames. Within six minutes of the time of discovery, the total casino area was involved in fire, at a burning rate of approximately 15 to 19 feet per second! The Clark County Fire Department received the call reporting the fire at 7:17 a.m. Captain Rex Smith, Engineer Chad Marshal, and Firefighters Bert Sweeney, Toby Lamuraglia, and Ted Singer arrived in Engine 11 at 7:19 a.m. They positioned the 1,500 GPM fire engine at the North entrance of the casino and implemented the High Rise Preplan. Upon entering the casino, the crew observed black smoke emitting from the Deli. They were only forty feet into the hotel when a huge fireball burst out of the Deli and rolled into the casino, hustling the crew out of the building. The company made it back to the engine as the flames sprang out the front of the entrance. Based on investigations by the Clark County Fire Department (CCFD) and the National Fire Protection Agency (NFPA), several likely causes were identified for the MGM Grand Hotel fire. On the most superficial level, the most likely source of the fire was:
“Heat produced in the west wall partition of The Deli serving station as a result of electoral short-circuiting (a ground-fault) of an ungrounded electrical circuit conductor to a flexible metal conduit… The wiring was an extension of original wiring in the serving station and provided power to the refrigerator compressor unit and evaporator fan of a pie case located on the north wall of the station.“ (NFPA, 1982).
This condition was caused by three prime factors- improper grounding, improper installation, and galvanic action. Further investigation by the NFPA and CCFD revealed that no dedicated equipment grounding conductor was found within the flexible conduit; therefore, it is assumed that all grounding was intended to be handled by the flexible metal conduit, electrical metal tubing, and receptacle box. Any discontinuity in this chain would lead to a scenario in which arcing currents would be possible. In one instance, it was noted that the aluminum flexible metal conduit itself was not properly connected to a receptacle box, and in turn the entire system was not properly grounded as shown in Detail B of Figure 3. (NFPA, 1982).
Galvanic Action
An investigation in greater detail by the Clark County Fire department documented that within the pie case near the compressor, portions of the aluminum flexible metal conduit came into contact with copper piping carrying refrigerant to the compressor shown in Figure 3. The vibration of the compressor allowed for increased contact between the two metals and facilitated a process known as galvanic action or galvanic corrosion between the two materials.
During this process, a small current is generated between the two materials and over time one metal will typically corrode at a faster rate than the other. Based on the Fourteenth edition of the Fire Protection Handbook (NFPA), “Aluminum carries a potential of + 1.7 volts while Copper carries -.34 volts,” signifying that the aluminum would corrode much sooner than the copper. This would create two potentially dangerous scenarios: a break in the grounding path, and the exposure of electrical conductors within the conduit (CCFD).
Improper Installation
When installing conductors in a conduit, it is common to pull them through the length of the conduit. Any excessive abrasion due to irregularities in the interior surface of the conduit (more likely along the segments of the flexible conduit) would lead to the abrasion and eventual degradation of conductor insulation. Over time, temperature cycling of the conductor, conduit, and insulation could lead to portions along the wire where the insulation of the wire is worn away and the conductor could potentially transfer current to the conduit itself (CCFD). The additional wire powering the pie case was also improperly installed, and gaps in the flexible conduit existed in the ceiling plenum and in the wall as shown in Fig. 3 Details A and B.
Ignition
When the three causes above were acting in unison, a dangerous combination was present. The galvanic action near the floor at the compressor corroded the flexible metal conduit over time. Heat from the compressor consistently pre-heated the conductor insulation, providing a lower required temperature from the conductor to wear away the insulation. It is then highly likely that uninsulated sections of wire formed over time, and the conductor came into contact with the flexible metal conduit. This contact energized the flexible metal conduit, and arc currents were then able to be formed across the disconnected portion of conduit from the improperly installed pie case wiring (CCFD, 1981).
According to the Clark County Fire Department investigation, the construction materials chosen in this location gradually emit more and more flammable gases as they age. After approximately six years, enough flammable gases were present in the area to allow the arc current to ignite. Fuel sources were then readily available in the kitchen and restaurant spaces, and the fire was subsequently able to propagate at a rapid pace.
Propagation
The fire began to spread throughout the ceiling plenum via conductive and convective heat transfer. Once the fire spread above the restaurant seating area, the ceiling plenum had become hot enough to ignite the furniture in the space via radiation (CCFD).
The lack of consistent slab to slab, full-height partitions allowed the flames to have a ready supply of air and a quick path out to the casino floor. Similarly, this allowed a free path for smoke to travel throughout the casino and interstitial levels. Smoke was able to penetrate seismic joints and unsealed areas in supposedly smoke-proof fire stairwells. Improper material selection on the smoke-proof stairwells allowed fire to burn through the walls in a relatively short amount of time, ultimately providing another direct path for smoke and fire (NFPA, 1982). Egress and Aftermath
Casino guests were evacuated almost immediately after flames were spotted in the Deli. According to several staff on duty, a fire alarm was said to have been activated but no such alarm was heard by other staff members or guests in other regions of the hotel.
The main egress paths are depicted in Fig. 4; all but stairway E2 provided direct access to the exterior of the building (NFPA, 1982). Stairways at the end of each corridor were considered smoke-proof with respect to their construction- in addition, all of these doors locked from the inside after they closed to prevent access to other floors from the stairwell for security purposes.
In total, 85 people were killed during the fire from smoke and carbon monoxide inhalation or other fire-related causes. The overwhelming majority of these fatalities were in the guest rooms or in circulation areas that were close to the unsealed seismic joints at the core of the building where smoke transmission would have been the worst, shown in Fig. 4. The lack of widespread fire alarm usage throughout the hotel can most likely attribute to the deaths that occured in rooms farther away from the central core. (NFPA, 1982).
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