BY TOM WELCH
In April 2006, Marin County, California, experienced several days of rain which, according to the National Weather Service, totaled in excess of 157 percent of the normal level.1 Local flooding occurred throughout the region, leaving the ground completely saturated. On April 11, 2006, a weather system hit the coastal county, stalled at landfall, and quickly dropped approximately three inches of rain.
At 0309 hours on April 12, 2006, an engine from the Mill Valley (CA) Fire Department responded to a code-2 for a public assist to aid an elderly male in clearing debris from a culvert that runs directly behind and under his residence. Rain, narrow streets, route selection, and poorly parked cars slowed the response to the residence, which is served by a steep one-lane road. Approximately eight minutes into the engine response, dispatch reported that the police department was on-scene and that a major mudslide had occurred.
On arrival, a distraught elderly female met the engine in front of her residence and reported that her husband was working below the bedroom sliding door at the rear of the house clearing debris from the culvert when mud crashed down the hillside into the structure.
From the A side of the house, it appeared that the two-story, split-level, single-family residence had muddy water running through the garage. On further inspection of the C side of the structure, we saw mud surrounded by large uprooted oak trees stacked to the roofline intruding into the rear of the home. The debris field extended approximately 150 feet from the house back toward the head of the slide, which was almost 60 feet wide (photo 1).
 (1) The Mill Valley mudslide as seen from the B and C sides of the structure. (Photo by Mike Lennon.) |
The affected residential structure, built in 1963, was located at the base of a box canyon and a steep drainage culvert that ran under the house to the road below.
The first engine officer of the first-arriving engine was concerned with the safety of his crew and the potential for additional slides. The lookouts, communications, escape routes, and safety zones (LCES) mnemonic, commonly employed in a wildland fire setting, proved to be very relevant at this dynamic scene.
Early in the incident, the engine company officer requested additional units to the area above the slide to assess the situation from a different perspective and to become lookouts. The incident commander established communications using command and tactical frequencies accessible to all responding county units. He further announced escape routes located behind the structure and established safety zones that could be continually evaluated throughout the incident.
PERSONNEL A KEY ASSET
Arriving officers initially understood that personnel was a key asset in facilitating the rescue of the buried victim. No one knew just how many responders would be required. The on-duty battalion chief and the Mill Valley Police Department on-duty supervisor formed a unified incident command team (Mill Valley Fire BC, Mill Valley PD). They requested dispatch to fill the first alarm, a response that included two additional Type 1 engines and one advanced life support (ALS) ambulance.
The Marin County urban search and rescue team (Marin US&R, California Regional Task Force 1) joined the response. Because of the weather and the potential for additional, similar incidents, two of the Marin US&R vehicles had been staffed and prestaged throughout the county. The responding Marin US&R team included a structural engineer, who added a significant level of competence in assessing the structure’s stability. The unit also added a predetermined command structure to the significant human resource capability already at the scene. On his arrival, the scene’s incident commander (IC) immediately established the Marin US&R task force leader as the Operations Section chief, which enabled the IC to better supervise the entire scene.
Staffing proved to be an issue throughout the incident. The working conditions were strenuous, described by many as extremely fatiguing. A few minutes before 0800 hours, an unprecedented request went out to all fire departments within Marin County for two available off-going staff members to report to staging for assistance needed for the second operational period. This request netted approximately 20 additional personnel.
In addition, two California Department of Forestry and Fire Protection Type 1 hand crews and one local conservation crew were called to the scene. Using buckets and shovels took a toll on the responders, who required frequent rest periods. As staff was added, logistical support became necessary. This need was filled through the Marin County US&R team’s logistics officer with assistance from the American Red Cross.
HIGH GAS LEVELS LIMIT INITIAL SEARCH
Initially, search operations were limited by extremely high natural gas levels found within the structure. Shutting down the gas at the meter and pressurizing the open skylights and windows with positive-pressure ventilation mitigated the unsafe atmosphere. These actions took approximately two hours to complete before interior rescue operations could commence. Initial arriving units conducted limited searches in the last known victim location on the C side of the residence.
First, they searched void spaces within the structure. Through good intelligence-gathering activities, it was determined that the last-known victim location was the victim’s bedroom. This prompted a focused-area search and proved instrumental in locating him. Operations initially were very low tech. Buckets, shovels, and scraping tools were used inside the victim’s bedroom, bathroom, and closet (photo 2). Chain saws facilitated access to the flat roof over the victim’s suspected location.
 (2) Buckets, shovels, and scraping tools were used inside the master bedroom and closet. (Photo by Rich Lopez.) |
During the early-morning hours, K9 search teams and cadaver-locating dog teams arrived. The animals were used throughout the structure, reporting “soft hits” to the C side of the structure and in the victim’s bedroom. The initial inclination of the command staff was that the victim had been pushed through the exterior wall into the bedroom on the C side and was either in a void space or under 12 feet of mud. Excavation was difficult because of root balls, extensive mud, and newly created confined spaces.
On evaluation, it appeared that obvious structural damage was confined to the C side. Interior rooms adjacent to the C side were affected only by mud. Windows and doors moved freely throughout the building, suggesting that the structure was not raked or leaning from one side or the other and that the structure stood firm on its foundation.
The structure told a story of the incident, how it survived and how it could respond to a second mudslide. The structure also acted as a debris flow dam that prevented further downhill mudflow. Although firefighters are well versed in safety considerations, they lack an engineer’s education and experience. Therefore, the US&R structural engineer’s vigilant evaluations of scene dynamics added a significant safety factor and an important perspective.
DIVERTING WATER SPEEDS THE RESCUE
As the search ramped up, it became clear that diverting water around the structure would hasten the rescue operation. Under the authority of Mill Valley, a private contractor was brought in to divert water around the structure through the development of check dams and a strategically placed culvert system. Communications among the city, private contractors, and the incident’s unified command team seamlessly occurred. This success was due in part to good previously established working relationships.
The second operational period of the first day saw the transition from a verbal to a written incident action plan. This plan included incident objectives of “safety, stabilization of debris flow, victim location, and recovery.” Over the next three days, incident action plans were effective in carrying out these objectives. Early into the event, it was decided that multiple operational periods within each day would be necessary.
Suspected slides or pile movement on the first day resulted in several evacuations from the rescue area. No large-scale slides occurred, but the frequent evacuations triggered the development of a risk/benefit analysis by the command staff. By this time, a complete search of the interior of the structure and the void spaces established that no human-sized survivable voids remained.
It became increasingly risky to continue rescue operations. With continued rain showers and mudflow pressuring the C side of the structure, approximately 12 hours into the incident, the command staff officially declared the scene a recovery instead of a rescue. Some crews were released as the US&R and fire rescue teams reorganized into salvage and recovery roles. This declaration also allowed for an extensive safety evaluation of the working areas on the C side of the structure.
RESCUE OPERATION CONVERTS TO RECOVERY
The first action of the recovery mission was salvage. To limit further damage, the entire contents of the structure were removed and stored off-site. Second, a 70-ton hydraulic crane was brought onto the scene. The crane and its transport required additional expertise, including scouting the route and understanding the specifications of the equipment. The 70-ton “all steer” crane, with a half-yard bucket and an ability to choke loads, proved to be the proper selection for this incident.
The original first-operational-period crews were brought back to the scene for the third operational period, and the second-operational- period personnel were released with orders to prepare to return the next day. Rigging, cutting, and search teams worked closely with the crane to remove debris and zero in on the victim’s location.
The initial goals for crane operations centered on debris removal from the C side and the master bedroom area. The team accomplished this task by removing the roof sections over the bedroom and the nonsupportive walls within that area. Again, the structural engineer proved very helpful, adding a significant safety component to these operations.
Debris was loaded into 10-yard trucks and hauled off-site, since the incident size and location did not allow for on-scene relocation. Because of working conditions and the high potential for injury, incident operations concluded at 2318 hours on the first day. Start-up time was established at 0700 hours for the first operational period of the second day.
The first operational period of the second day proved to be one of slow digging. The half-yard bucket allowed for more precise digging over the suspected victim’s location; however, the crane swing and the process of dumping into the trucks slowed operations. At this time, preincident photos became available showing the backyard, stem wall, and culvert prior to the slide (photo 3). These pictures allowed for an even more precise victim digging location. After approximately 27 operational working hours (excluding night downtime), crews finally located the victim.
 (3) Preincident photos showed the backyard, stem wall (outside load-bearing wall on raised foundation), and culvert prior to the mudslide. (Photo by Greg Moore.) |
RECOVERY TAKES LONGER THAN EXPECTED
At first, the recovery team provided the IC with an estimate of two hours for victim removal. Additional segmented “two-hour” estimates continued for eight hours until these time estimates were abandoned. These estimates created problems for the incident’s public information officer because the media sought information and a conclusion to the incident. The understandably “loose” recovery time estimates perhaps resulted in a public perception of confusion.
Extricating a mudslide victim is more difficult than one might expect. The victim’s lower appendages were pinned between the stem wall and the mud. A massive amount of pressure and suction were holding the limbs against the wall, slowing progress. As the dynamics of the slide changed, the IC had to reevaluate scene safety.
The mud kept coming down the hillside. Many rescuers likened the situation to mopping back the sea, one bucket of mud taken out while two buckets fill in. Into the second night, a constructed box (photo 4) was placed around the victim to create a safety zone for the recovery team should a second slide occur. Fading light and the limited ability to monitor future slides necessitated stopping operations at 0230 hours.
 (4) A construction box was placed around the victim to create a safety zone for the recovery team. (Photo by Eric Oyen.) |
The third day presented new challenges and strategies for victim removal. The previous day’s operations involved digging straight down near the victim. Continuous mudflow and suction made the results unsuccessful. The new strategy was to dig back from the victim’s location to attempt to reduce the force exerted by the downward mudflow. This action reduced the force of the mudflow, but the prior removal of several trees and their root balls actually destabilized the mudflow. The subsequent slide movement caused a separation of the water-diverting culvert that sent additional mud and water into the scene, further complicating operations.
Application of water through a piercing nozzle was attempted to release the suction that held the victim in the mud. It was unclear whether this method was effective, perhaps because the water pressure was inadequate. Continuously working, a squad of more than eight people took approximately eight hours just to free the victim’s left leg. These efforts attest to the difficulties of working in mud while flow continues.
Eventually, the victim’s second leg was freed, and the victim was extricated from the mud. Crews were immediately decontaminated at the end of the third day. A brief post-incident session was conducted, the equipment was gathered, and the incident command was terminated.
EVALUATING WHAT WENT RIGHT
Incident safety was stressed throughout this mudslide incident. However, safety improved when the decision was made to shift the incident from a rescue to a recovery. It appeared that staff took fewer risks and were more willing to rotate to rehab.
The posting of lookouts with air horns for additional slides provided advanced warning to rescue staff in the so-called danger zone. Consider frequent rotation of staff to reduce fatigue and improve vigilance when watching an active slow-moving debris field.
As the incident progressed, escape routes toward safety zones were well established. Although they were re-evaluated throughout the incident, safety zones did not change much, as digging efforts were focused in specific areas. Communications were continued from previous operational periods: One blast of the air-horn required a stop in work and visualization of the debris flow and the canyon above. Three blasts required an immediate exit from the digging site to the safety zones. Throughout the incident, there were three fully successful and accountable evacuations. The use of LCES ensured the safety and effectiveness of the incident response.
Stabilization of the debris flow proved more challenging than had been anticipated. One of the first steps in accomplishing this objective was to divert water from the canyon around the digging and the suspected victim location. The strategic placement of check dams above the incident allowed for diversion of water from the rescuers. This reduced the liquidity of the flow, allowing for enhanced rescuer efficiency and effectiveness in the digging area.
On the third operational day, work ceased when one of the culverts gave way as a result of digging and slide activity, sending a river of muddy water through the work area. Restoring the dams and diverting the water around the incident site mitigated this issue. In an effort to stem the flow of water and mud, temporary retaining walls were placed above the victim’s location to maintain a more tolerable working environment.
However, both retaining walls proved ineffective (photos 5 and 6), as evident from the initial starting point of the walls compared with the box location (victim location, photo 5) and the location of the walls in relation to the box just a few hours later (photo 6). In hindsight, posts for a temporary retaining wall should have been anchored into the ground below the slide. It is very difficult to know just how deep to place the posts or if this is even a viable option for this type of incident.
 (5) Retaining walls were ineffective in protecting the construction box for an extended period. |
 (6) In just a few hours, the initial distance from the box to the wall closed considerably. (Photos by Rich Lopez.) |
A major issue in this incident was monitoring the debris flow, which can be “an unhurried killer.” Monitoring a slow-moving debris flow is like watching water boil: The process can only be evaluated over time.
The monitoring of the debris flow could better be served through enhanced technology. Lasers, survey equipment, or global positioning system (GPS) units could have made debris-flow surveillance easier and more effective. Meanwhile, a low-tech measure is suggested for future incidents: Stretch a line across the debris flow between two fixed (nonmoving) points. Place flags on posts strategically positioned in the debris flow in relation to the line. Based on the assessment of the flags and their relationship to the line, you can evaluate flow progress.
This low-tech solution also enables quantifiable measuring of the rise of the flow and the downward motion of the surface flow. The limitation of this technique is that it measures only the surface flow. This incident made clear that surface flow and subsurface flow are not always the same. The surface of the slide could appear stable while the subsurface seeps into the scene without restraint and detection.
Monitoring the rise and fall of the debris flow is as important as monitoring the direction of flow. The rise and fall of the debris flow inform the observer of the pressure exerted from the down forces behind the flow. Similar to watching an ocean wave and its rise just prior to landfall, mud flow also rises when it reaches an obstacle-in this case, a residential structure. It was observed several times throughout the incident that even though the surface of the flow appeared to move only a small distance down the hill, the subsurface of the debris flow brought yards of mud into the workspace. Here again, a drawn line across the incident with flags could give the observer a hint of the debris flow and the amount of exerted pressure.
Using a hydro-vac truck was considered early in this incident. Personnel from the Mill Valley Department of Public Works were on the scene evaluating the potential. However, they advised against employing their hydro-vac truck because of access issues and the vehicle’s limitations. It appears that future incidents of this size and scope would benefit from this technology.
Medical care for the rescuers is vital in any operation. In this incident, full decontamination was not required for all rescuers prior to leaving the incident; the only comprehensive decontamination was conducted at the end of the third day. The usual hazards presented, and appropriate precautions were taken. However, full decontamination should have been mandatory for all operational rescuers at the end of their work cycle, especially prior to mealtime.
It took 171 personnel more than 62 hours to recover the victim from the Mill Valley mudslide. The incident concluded with no rescuer injuries or known resulting illnesses. However, this incident was considered by many to be a true “near miss.” If the response had been at a different time or of a different duration, the Mill Valley Fire Department and the other responding agencies could have suffered casualties. The Mill Valley Fire Department prides itself on customer service and community relations. No one in the department would hesitate to assist an elderly man in clearing his culvert to minimize damage to his residence or health. Perhaps this incident’s most important lesson is this: Vigilance and planning are essential to protecting rescuers from death and injury.
Special thanks to Battalion Chief Mark Brown, Dr. Jim Pointer, M.D., and Captain Brent Chadwick.
Reference
1. Doyle J., Fernandez E., “Slide tragedy in Marin,” San Francisco Chronicle; April 13, 2006.
TOM WELCH has served five years as an engineer paramedic for the Mill Valley (CA) Fire Department and has approximately 15 years of experience in the fire service. He is a member of the Marin County Urban Search & Rescue Team, serving as the medical team manager.
