Chapter 3.pdf

Western Canada Mine Rescue Manual Chapter 3 Environmental Conditions 3-1 OBJECTIVES Mine rescue teams should be aware of the special dangers associated with environmental conditions. This chapter will provide a basic understanding of:  Avalanche terms, concepts, and equipment  Ice travel  The...

Western Canada Mine Rescue Manual Chapter 3 Environmental Conditions 3-1 OBJECTIVES Mine rescue teams should be aware of the special dangers associated with environmental conditions. This chapter will provide a basic understanding of:  Avalanche terms, concepts, and equipment  Ice travel  Thermal stress CONCEPTS AND DEFINITIONS Mines operating in avalanche-prone areas must develop an avalanche emergency response plan tailored to their mine. Mine rescue personnel may be required to perform emergency response activities that expose them to avalanche hazards. This chapter is intended to only provide basic avalanche awareness. A qualified avalanche safety officer must be identified, consulted, and lead the safe emergency response in an active avalanche situation. The avalanche safety officer must conduct an avalanche risk assessment and establish active avalanche safety measures prior to planning emergency operations. An avalanche is a rapid flow of snow down a sloping surface that can occur at any time provided the right conditions are present. Avalanches have three main parts:  Starting zone (point of origin): Where the unstable snow first breaks away. An avalanche path may have several starting zones. Characteristics of starting zones include: incline, slope aspect, exposure to wind, elevation, exposure to sun, natural ground condition.  Track (zone of transition): Below the starting zone, where the avalanche accelerates and typically reaches maximum destructive potential. It will have the potential to overrun terrain features and previous avalanche tracks. Avalanche areas can contain one or more tracks. These tracks may be poorly or clearly defined.  Run-out zone: Where the avalanche decelerates and finally comes to rest. It can be identified as a zone where the bulk of the snow is deposited. Avalanches may occur anywhere given the following conditions:  Geography, such as the natural topography of the area, engineered land forms, and slope orientation.  Snow accumulates on a moderate to steep slope (30°–45°). Avalanches rarely start on slopes steeper than 45° as snow sloughs off continuously rather than accumulating.  Snow conditions, such as: o Snow pack (accumulation) o Mass o Layers of snow and bonding between facet Fig 3.1 Slope steepness and avalanches layers o Environmental effects: Variation in temperature, wind, humidity 3-2  An external event that triggers the slide. These can be: o Natural: New snow, transported snow (wind), temperature changes, sun, rain, thawing and animals. o Human: Explosives, working on a slope, working below a slope, mobile equipment, and recreational activities. o Trigger points: Snow conditions, shallow areas/variable depth snow packs, points of weakness (e.g., trees, rock outcrops) may all contribute to the development of avalanche conditions. Two types of avalanche are commonly recognized: Loose Snow Avalanches may consist of dry powder snow or wet snow. Dry snow avalanches are most common in winter after storms and rare in spring or summer. Wet snow avalanches consist of heavy, wet, sun-heated or rainrotted snow or wet new snow and are most common in spring and summer, particularly on south-facing slopes. These avalanches:  Start from a point  Are set in motion progressively  Require snow with poor cohesion, similar to that of dry sand  Are usually confined to surface layers and therefore relatively small Slab Avalanche Loose Snow Avalanche Slab Avalanches occur when a slab of fairly cohesive layers of snow, poorly bonded to the snow underneath, breaks off along a fracture line. These avalanches are by far the most dangerous. They are set in motion simultaneously, over a large area and may start in either shallow or deep snow layers. Safety in Avalanche Zones The successful rescue of a person buried in an avalanche very often depends upon actions taken by unburied survivors. Teams performing rescue operations in an avalanche area must be mentally prepared for the possibility that they too may be overtaken by an avalanche. If crossing an avalanche track cannot be avoided, take the following precautions:  Select the shortest possible route high on the slope or low in the run-out zone  Plan an escape route.  Wear mitts and hats. Tighten clothing and smaller packs. Loosen larger packs in case they need to be quickly removed.  Assign a spotter at the top and bottom of the track and agree on a warning signal.  Cross quickly. If the crossing is narrow, one person crosses at a time. Otherwise, maintain space between rescuers to minimize the risk of exposure to an avalanche track. 3-3 AVALANCHE RESCUE GEAR Probe, Avalanche transceiver (beacon), and Shovel: These three items work together and are the minimum required equipment for every avalanche rescuer. For proper use of avalanche rescue gear, refer to manufacturer’s guidelines. L-R: Probe, Shovel, Transceiver (bottom) ICE TRAVEL Some mining operations in remote northern locations are accessed by ice roads built on frozen lakes and rivers. Prior to travelling on ice The thickness of the ice must be tested frequently in various locations. The smallest thickness is what is used to determine the strength of the ice. Table 3.1 indicates the weight that will be supported by varying thicknesses of clear blue lake-ice, provided the load remains in motion.  Type of ice: o River or lake (movement of water beneath ice). Clear blue river-ice, with moving water beneath it, is not as strong as lake-ice. Loads should be reduced by at least 15% o Clear or natural ice (black or blue hue). This is considered the strongest form of ice. o Slush ice (white hue) is snow saturated with water. It is commonly found as new ice floating after a heavy snowfall. It is much weaker than clear blue lake-ice.  Cracks in ice may affect its ability to support a load. While traveling on ice  As a vehicle travels on ice it creates a resonance wave in the underlying water. The weight and speed of the vehicle, as well as the depth of the water, influence the size and speed of the wave. The resonance wave can affect the strength of the ice, potentially resulting in a blowout, or an ice failure.  Unless otherwise posted, the speed limit on ice roads is 25 km/h for a loaded vehicle and 35 km/h for an empty vehicle. 3-4 The following table shows the maximum allowable mass of a vehicle in motion for ice of various thicknesses. Gold’s Formula for determining the maximum allowable mass is: 𝑀 = 4 × ℎ2 where M is the mass of the vehicle (kg) and h is the thickness of the ice (cm) Ice Thickness (cm) 2.5 3.5 5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35 Ice Thickness – Clear Blue Lake Ice Capacity (kg) Ice Thickness (cm) Capacity (kg) 25 37.5 5,625 49 40 6,400 100 42.5 7,225 225 45 8,100 400 47.5 9,025 625 50 10,000 900 52.5 11,025 1,225 55 12,100 1,600 57.5 13,225 2,025 60 14,400 2,500 62.5 15,625 3,025 65 16,900 3,600 67.5 18,225 4,225 70 19,600 4,900 72.5 21,025 Ice Thickness (cm) 75 77.5 80 82.5 85 87.5 90 92.5 95 97.5 100 102.5 105 107.5 110 Capacity (kg) 22,500 24,025 25,600 27,225 28,900 30,625 32,400 34,225 36,100 38,025 40,000 42,025 44,100 46,225 48,400 Table 3.1 – Ice Strength 3-5 THERMAL STRESS Thermal stress refers to a range of physiological reactions to adverse temperature conditions. There are many factors that contribute to these stresses. Mine rescuers must be able to recognize and adequately respond to these conditions. Hypothermia is a condition of lowered internal body-core temperature (exposure sickness). Failure to recognize symptoms of hypothermia is the leading cause of death for people in the outdoors. Hypothermia is caused by overexposure to a cold environment and can develop very quickly if proper precautions are not taken. Hypothermia results from chilling by cold, wind, or water such that the body loses heat faster than it can produce it. Factors contributing to the development of hypothermia include:  Inadequate clothing  Alcohol or drugs in the body Hypothermia and Water Immersion  Wetness (perspiration, rain)     Exhaustion, dehydration, and lack of nutrition Wind and water Temperature Duration of exposure Symptoms of Hypothermia Visible symptoms indicate the onset of hypothermia. Its advance is marked by recognizable stages. Stage Core Temperature (C) Mild Hypothermia 37.2–36.1 36.1–35.0 Moderate Hypothermia 35.0–33.9 33.9–32.2 Severe Hypothermia 32.2–30.0 30.0–27.8 27.8–25.6 25.6–23.9 If water temperature (C) is... 0 1–5 5–10 10–15 15–20 20–25 25–30 Exhaustion or Unconsciousness < 15 minutes 15–30 minutes 30–60 minutes 1–2 hours 2–7 hours 3–12 hours Indefinitely Expected survival time 15–45 minutes 30–90 minutes 1–3 hours 1–6 hours 2–40 hours 3 hours–indefinitely Indefinitely Signs & Symptoms Normal, shivering can begin Cold sensation, goose bumps, unable to perform complex tasks with hands, shiver can be mild to severe, hands numb Shivering, intense, lack of muscle coordination becomes apparent, movements slow and labored, stumbling pace, mild confusion, may appear alert. Use sobriety test: if unable to walk a 30 foot straight line, the person is hypothermic. Violent shivering persists, difficulty speaking, sluggish thinking, amnesia starts to appear, gross muscle movements sluggish, unable to use hands, stumbles frequently, difficulty speaking, signs of depression, withdrawn. Shivering stops, exposed skin blue of puffy, muscle coordination very poor, inability to walk, confusion, incoherent/irrational behavior, but may be able to maintain posture and appearance of awareness Muscle rigidity, semiconscious, stupor, loss of awareness of others, pulse and respiration rate decrease, possible heart fibrillation Unconscious, heart beat and respiration erratic, pulse may not be palpable Pulmonary oedema, cardiac and respiratory failure, death. Death may occur before this temperature is reached. 3-6 Bodily Heat Loss The head and neck are the most critical heat-loss areas. Other body areas have high rates of heat loss while a subject is holding still in cold water. Infrared pictures show that the sides of the chest (where there is little muscle or fat) are the major routes for heat loss from the warm chest cavity. The groin area also loses much heat due to the large blood vessels near the surface. If an effort is made to conserve body heat, these regions deserve special attention. Fig 3.2: This infrared image of a body shows high-heat areas (red) and low-heat areas (blue) Cold Water Survival Techniques Mine rescuers that work near water require personal floatation devices (PFD). The onset of hypothermia is much quicker for people immersed in cold water. These two techniques can extend predicted survival times: H.E.L.P. (Heat Escape Lessening Position) This technique for cold water survival protects the parts of the body that lose heat fastest. It increases predicted survival time by up to 50%. This position requires a floatation device that maintains upper-body buoyancy. Huddle Position Predicted survival time can be increased by up to 50% if survivors huddle together. In this position, the sides of the survivors’ chests are held close together to prevent heat loss. In cold water (<10 C), the average person can swim no more than one-tenth the distance they can in warm water. 3-7 Cold Stress Conditions Exposure to cold environments or water for a prolonged period can result in a number of adverse conditions. Particularly during winter months, precautions should be taken to avoid these conditions during mine rescue work. Condition Chilblains Cause  Prolonged and repeated exposure for several hours to air temperatures from above freezing to as high as 16 C  Ear lobes, noses, cheeks, fingers, or toes are exposed to the cold and the top layers of skin freeze Symptoms (may or may not be present)  Affected skin area there will have redness, swelling, tingling, and pain Frostbite  Exposure to extreme cold or by contact with extremely cold objects (especially those made of metal). It may also occur in normal temperatures from contact with cooled or compressed gases.  Frostbite occurs when tissue temperature falls below the freezing point, or when blood flow is obstructed.  Mild cases: Inflammation of the skin in patches accompanied by slight pain  Severe cases: Tissue damage without pain, or there could be burning or prickling sensations resulting in blisters  Blood vessels may be severely and permanently damaged, and blood circulation may stop in the affected tissue  Frostbitten skin is highly susceptible to infection, and gangrene (local death of soft tissues due to loss of blood supply) may develop Immersion Foot/Trench Foot  Occurs when feet have been wet, but not freezing cold, for prolonged periods of time  Can occur at temperatures up to 10 C  Trench foot is more likely to occur at lower temperatures  Immersion foot is more likely to occur at higher temperatures and longer exposure times.  Hands can be affected if a person wears wet gloves for a prolonged period under cold conditions  Tingling and numbness  Itching, pain, or swelling of the legs, feet, or hands  Blisters  Skin turns red then blue or purple  Gangrene may develop Frostnip  Affected skin turns white and may feel numb.  Top layer of skin feels hard but the deeper tissue still feels soft 3-8 Heat Stress Conditions As with cold stress conditions, the severity of heat stress conditions depends on duration and intensity of exposure and activity, as well as the patient’s fitness and health. Condition Heat Rash Heat Cramps Heat syncope (fainting) Heat Exhaustion Heat Stroke Cause  Hot, humid environment  Plugged sweat glands  Heavy sweating from strenuous physical activity drains a person’s body of fluid and salt.  Fluid loss  Inadequate water intake  Standing still resulting in decreased blood flow to brain  Fluid loss and inadequate salt and water intake causes the body’s cooling system to start to break down.  If a person’s body has used up all its water and salt reserves, it will stop sweating. This can cause body temperatures to rise.  Heat stroke may develop suddenly or may follow from heat exhaustion. Symptoms (may or may not be present)  Red bumpy rash with severe itching  Painful cramps occur in the most commonly worked muscles (arms, legs, abdominals)  Onset can be immediate or delayed.  Sudden fainting after at least two hours of work  Cool, moist skin  Weak pulse  Heavy sweating  Cool, moist skin  Elevated body temperature  Weak pulse  Normal or low blood pressure  Fatigue, weakness, nausea and vomiting  Thirst  Panting or rapid breathing  Blurred vision  Dizziness  Oedema  Light headedness  High body temperature (higher than 41 C)  Any one of the following may indicate heat stroke: o Hot, dry, flushed skin o Person is weak, confused, upset or acting strangely; o has hot, dry, red skin; o a fast pulse; o headache or dizziness.  In later stages a person may pass out and have convulsions  Fast breathing  Absence of sweating  Shock  Cardiac arrest 3-9 Wind Chill is the perceived decrease in air temperature felt by the body on exposed skin due to wind. It must be considered an additional hazard when working in cold environments. The wind chill table should be posted wherever the wind and temperature recorder is mounted. 3-10