January 2, 2006

Fire

Posted in Misc at 19:00 by graham

I went on a basic fire fighting course a long time ago. Here is a write up of the course notes:

Fire is a chemical reaction called combustion (usually oxidation) resulting in the release of heat and light. To initiate and maintain this chemical reaction – i.e. for the outbreak of fire to occur and continue – three elements are required, and the removal of any of these three will extinguish the fire:

  • Fuel: Any combustible substance either solid, liquid or gas. Starving a fire will extinguish it.

  • Heat: The attainment of a certain temperature (the ignition point). Once a fire has started it normally maintains its own heat supply. Cooling a fire will extinguish it.

  • Oxygen: This is usually in plentiful supply as it makes up one fifth of the air we breathe. Blanketing or smothering a fire will extinguish it.

    If the rate of heat generation is less than the rate of heat dissipation, combustion cannot continue. For instance if a match is applied to a block of wood, the heat from the flame is absorbed by the mass of the wood and the heat is insufficient to raise the whole block to its ignition temperature. If the block is reduced to shavings, the surface area of a single shaving is high in relation to its weight, and it will easily catch fire. Gases and flammable vapors are extremely dangerous because of their large surface areas. Water is normally used for cooling a fire as it has a great capacity for absorbing heat, and it is cheap and readily available.

Types of fire fighting equipment

Portable fire extinguishers are ‘first-aid’ fire fighting equipment; they have a limited duration of discharge, and are only for tackling small fires.

Water extinguishers (Red)

The most common type of extinguisher. For use on fires involving combustible materials, such as wood, paper, textiles and fabrics. They remove the heat from the fire by cooling. They should not be used on electrical equipment. To use:

  • Remove the safety pin or cap
  • Operate by squeezing the trigger of the grip mechanism or by striking the plunger
  • Direct the jet of water at the base of the flames
  • Keep moving the jet across the area of the fire in a sweeping motion
  • Only tackle small, minor fires

Carbon dioxide extinguishers (Black)

Best suited to fires in electrical equipment, but will also cope very effectively with flammable liquids. The extinguisher delivers a high concentration of carbon dioxide gas under pressure, producing inert vapor which excludes oxygen and smothers the fire.

The mechanism to operate is similar to that for trigger operated water extinguishers.

Dry powder extinguishers (Blue)

Best suited to larger flammable liquid fires, but can also be used on electrical fires. Powder is expelled from the extinguisher by means of gas pressure. Dry powder is very effective as a knock-down agent for flammable liquid fires (it is used by the fire service in road traffic accidents). However it is also very messy and can damage electrical equipment such as motors.

BCF or Vaporising Liquid extinguishers (Green)

Suitable for us on flammable liquid fires and on electrical fires. The liquid is stored in the extinguisher under nitrogen pressure. When it is expelled, it is vaporised by the heat of the fire producing a smothering effect by reducing the oxygen content. The vaporised liquid also interacts with the process of combustion chemically and this helps extinguish the fire.

Fire fighting

Most fires begin in a very small way and can be put out easily if some form of extinguisher is nearby and there is someone who knows how to operate it. However discretion is essential in deciding the lengths to which ‘first-aid’ fire fighting is carried out. If you do decide to tackle a minor fire follow these rules:

  • Take up a position where access to the fire is unrestricted but where a quick and safe retreat is possible. Outside, this means being up-wind of the fire.
  • Crouching will help the fire fighter to keep clear of smoke and avoid heat. It will also allow a closer approach to the fire.
  • Always ensure that the fire is completely extinguished and not liable to reignite or continue smoldering.
  • Once used an extinguisher should be sent to be recharged.

Spread of fire

Convection is the transport of heat by movement of the heated substance. Over four-fifths of the heat of the fire is carried away by air and other gases in this way. By being heated the air becomes less dense than the surrounding atmosphere and, mixed with gases produced by the fire, moves upwards forming convection currents which carry away with them heat and smoke. The temperature of this rising air is likely to be very high.

Radiation: Objects in the neighborhood of a fire are exposed directly to the radiant heat from its flames and burning fuel. The nearer these are to the fire the greater the intensity of the radiated heat reaching them and the more likely they are of heating to ignition point. This is what happens when clothes drying in front of a fire ignite.

Conduction: Although some metals such as steel will stand up to great heat without igniting, their presence, e.g. in girders or partitions, in a burning structure will not necessarily check a fire. Metal is a very good conductor of heat throughout its length and may cause combustible materials at its other end to smolder until they reach their ignition point. A metal door becoming heated may ignite materials in contact with its other side.

Concluding remarks

At work, at home, on holiday, in any building you occupy for longer than a few hours, ask yourself these questions:

  1. Where is my nearest fire alarm and fire extinguisher ?
  2. Do I know how to operate, and the use of, all the fire fighting equipment ?
  3. Do I know where the nearest fire exit and my assembly point is ?
  4. What action do I take on discovering a fire or hearing the fire alarm bell ?
  5. Do I know the evacuation procedure to follow ?

January 1, 2006

Fatigue

Posted in Behaviour, Strategy at 14:59 by graham

This is sourced from Naval Strike and Air Warfare Center; ??Performance Maintenance during continuous flight operations;?? published 01 Jan 2000; and from USAF School of Aerospace Medicine; ??Warfighter endurance management during continuous flight and ground operations??; published January 2003;

Before we start, we’ll need a couple of definitions. Continuous Operations: Operations that extend over 24 hours at a normal rate. Each individual works a usual amount of hours, and is relieved at the end of a shift to return later. As the operation runs round-the-clock an individual will work different hours which may conflict with circadian rhythms, and disrupt sleep patterns. Sustained Operations: Involve continuous performance longer than 24 hours. Work is continued until a goal is reached. Sleep deprivation is common. Prevalent in ground warfare.

After a night without sleep mental and motor skill performance degrades to that of an individual who is considered to be legally drunk, (i.e. blood alcohol content (BAC) of 0.10 %). Even 18 hours of wakefulness equates to BAC of 0.05%.

Sleep cannot be stored up prior to a continuous or sustained operation. Sleep loss, circadian rhythm disruption and hard work combine to produce fatigue. Fatigue is not due to lack of motivation or attitude. Fatigue needs to be managed.

The planning and organisation required prior to the start of an operation may mean a team is already tired. This is referred to as preload.

Prior experience with sleep loss does not provide training to maintain performance. Resistance to fatigue varies between individuals.

Combat naps, the military equivalent of a power nap, help to maintain performance. After a power nap, individuals may experience 5 – 20 minutes of sleep inertia characterized by confusion and sluggishness. Taking more naps (practicing) appears to reduce this problem. During sustained or continuous operations, power naps should be encouraged and sometimes mandated. Power naps should last less than 40 minutes from the time one begins to attempt sleep to the time of awakening. It is designed to be too short to allow the individual to enter slow wave sleep (SWS) and yet still get a brief, hopefully restorative, nap. The first SWS epoch occurs within about 60 minutes. Research suggests that these naps can provide between 2 to 4 hours of useful physical and mental activity, for about 2-3 days, sometimes longer. After a few days however, cumulative sleep debt would be overwhelming.

A short sleep is best when more time is available for rest during a mission but not enough for a full sleep. Short sleeps are recommended to be at least 3-4 hours in duration. They are designed to allow the individual to progress through and avoid the SWS epochs. These sleep periods can maintain useful waking performance levels for 4-10 hours and perhaps longer. Although few studies have been done, anecdotal military evidence suggests that 3-4 hour naps can maintain crews for 4-5 days before sleep debt becomes overwhelming.

The minimum amount of sleep required to maintain performance during sustained operations is 4 – 5 hours per day. Fragmented sleep is less effective.

A ‘normal’ sleep is generally accepted as being 8 hours. Whatever the length of sleep, it should occur in 90 – 100 minute increments to avoid awakening during the deeper stages of sleep. This will minimize sleep inertia. Sleep should occur at the same time every day (including weekends), in a dedicated, quiet and dark place.

Sleeping more than 10 hours may cause sleep drunkenness and should be discouraged, even after a period of sleep deprivation.

There are numerous cyclic body rhythms in humans that collectively are described as circadian rhythms. Isolated from all external clues, humans seem to operate on a 25 hour cycle. External clues such as light and darkness (the most powerful cues), sleep, meals, social activities and clocks, reset the biological clock daily.

Circadian cycle

On an average circadian cycle, performance peaks between 12:00 and 21:00 hours (normally around 16:00), and falls to a minimum between 03:00 and 06:00 hours.

Continuous or sustained operations, trans-meridian travel (jet lag) and sleep deprivation all force the rhythmic systems of the body to re-adapt. They become out of phase with local time and with each other. Some phases will be delayed and others advanced. Seven continuous days of shift work are required to adjust the body temperature cycle. A single period of night work, or seven in a row, is more easily tolerated than three of four consecutive nights (which starts the process of circadian desynchronisation). If a round-the-clock operation is needed teams should specialise in either days or nights.

Extroverts, younger people, and those living on a more regimented schedule tend to have an easier time adjusting. As a general rule the body will adapt 40 minutes/day when traveling east and 60 minutes/day when traveling west. Westward travel requires lest time to acclimate. Bright lights maintain alertness and are a strong factor in accelerating circadian adaption.

It is easiest to initiate sleep twice a day; in the early afternoon and just before normal sleep time. Alcohol, while initially relaxing, significantly worsens the duration and quality of sleep. Caffeine interferes with sleep, and prevents effective napping. A nap or short sleep is most effective during the low point of the circadian cycle (03:00 – 06:00 hours).

Fatigue is both physical and mental. Physical aspects involve a loss of the power of muscles and sensors to respond. Mental fatigue includes the subjective feeling of weariness followed by worsening performance of cognitive tasks. This subjective sense of fatigue is the first indicator that people are getting tired. A useful external indicator is that the fatigued person loses their sense of humour.

During the Falklands conflict sedatives were used by the British to regulate sleep for pilots. Amphetamines were used by the British and Germans in WWII. During Vietnam both the American Air Force and Navy made amphetamines available to aviators. Intermittently since Vietnam up through Desert Storm the Air Force has used both amphetamines and sedatives in selected aircraft for specific missions. A combination of dextro-amphetamine (Dexedrine) and scopalomine are used by the Navy and NASA to combat motion sickness.

5mg of dextro-amphetamine (Dexedrine) help maintain alertness without causing other changes in mood and perception. 200mg caffeine compares favorably to amphetamine in improving cognitive performance but is less effective in maintaining alertness. 5mg of Dexedrine can be taken every 2 hours if required; dose should not exceed 30mg per 24 hour period.

Benzodiazepines produce the ‘most natural’ quality of sleep, and are used as sleep initiators. 5mg of zolpidem (Ambien) or 15mg of temazepam (Restoril) is used as an aide to sleep. A 7 – 8 hour period of restriction from higher cognitive activities is needed after taking this medication. No more than 10mg of zolpidem or 15mg of temazepam can be taken per 24 hour period.

Medication should be tested prior to it being needed, to allow individuals to adapt and gain familiarity with it. The Navy states that the use of stimulants or sedatives is appropriate only in combat or during exceptional circumstances of operational necessity.