Fire prevention and occupational safety part 2

In the previous edition of the Mena Infra magazine, we talked about the concept of fire prevention that involves a permanent reduction of Oxygen within a specific enclosure.

Having described the concept of fire prevention and made comparison to the more conventional, fire extinguishing methodology that employs gaseous suppression systems, we began to look more closely at the effects of lowering Oxygen levels on the human body, better known as "Hypoxia".

In this edition, we continue the topic from where we left off in April.

Hypoxia means a shortage of oxygen - as compared to anoxia, which means a total lack of it. In common with other mammals, humans have evolved with a system of breathing and blood circulation, which allows intake of oxygen from the air and its transport throughout the body.

Our body tissues need to extract oxygen constantly from the blood, at a basic rate for their metabolism, as well as the additional Oxygen needed for work and exercise.

Our bodies are accustomed to a certain level of oxygen being available in the immediate environment. The body can however compensate to some extent for a decreased level of Oxygen supply, but life remains dependant on maintaining an adequate supply of Oxygen.

Different organs and tissues can survive lack of oxygen for varying lengths of time: of all our organs, the brain is the most rapidly and irrevocably damaged by severe Oxygen starvation. Because the brain regulates both our breathing and blood circulation - the means by which oxygen is supplied to the whole body - deprivation of Oxygen to the brain will prevent restoration of the Oxygen supply as a whole; a potentially lethal vicious circle.

Hypoxia can occur for a variety of reasons:

1. when there is less than the normal amount of oxygen in the air inhaled;

2. when breathing is obstructed, is inadequate, or stops;

3. when oxygen is not transferred normally from the lungs to the blood;

4. when the blood cannot carry its normal quota of oxygen;

5. when the flow of blood is inadequate, or stops.

The air inhaled may provide insufficient oxygen either because the atmospheric pressure is low (at high altitude) or when the supply of fresh air is restricted. At high altitude the air is 'thinner' in that every molecule of the gas occupies a larger volume. The blood leaves the lungs carrying less oxygen than normal, therefore the tissues are exposed to a lower oxygen level.

If this is not too profound, the tissues can still obtain oxygen at the required rate, at least for resting metabolism, because the rate of flow of blood can increase. The tissues are living at a lower Oxygen level but are still getting a sufficient oxygen supply.

When the supply of fresh air is restricted, for example, by placing a bag over the head, or through confinement in a small enclosed space, or even in a larger enclosed space crowded with people, Oxygen is progressively depleted and exhaled carbon dioxide accumulates.

In some circumstances there may be displacement of air by other gases, and the effect of irritant or toxic gases, such as smoke, Chlorine, or Sulphur Dioxide, can complicate the effects of displacement of oxygen. This can occur for example, when a person remains in an enclosed space that is subjected to the Oxygen depletion effects of a gaseous fire suppression system, while at the same time being exposed to the smoke and toxic gases produced by the fire prior to suppression taking place.

Typical of Hypoxia, the haemoglobin in the arterial blood is less than fully saturated with oxygen. The redness of blood depends on this saturation. In hypoxia it becomes more blue, and cyanosis is the outward and visible sign of this when blueness tinges the skin.

The body has ways to defend itself against hypoxia at each stage of the process of oxygen acquisition: by breathing harder, to get more into the lungs; by crowding more red cells into the blood so that it can carry more in every circulating milliliter; by pumping the blood around at a greater rate; and by widening the blood vessels which supply the vital organs. Most of these adjustments can be made very rapidly.

When oxygen is low - but tolerably so - in inhaled air, and hence in the blood, the arterial chemoreceptors - being minute structures in the neck - sense this and, via the brain, cause a reflex increase in breathing. This brings the oxygen concentration in the lungs closer to that of the outside air - it remains low, but not as low as it would be if the breathing did not increase.

Stimulation of breathing occurs more dramatically when carbon dioxide is accumulating in the blood whilst oxygen is decreasing, such as in the example of breathing in a confined space.

If hypoxia of a tolerable degree is sustained for weeks, the bone marrow produces extra red blood cells, resulting in polycythaemia. The greater density of red cells brings the oxygen concentration in the blood back towards normal despite their haemoglobin carrying less than it ideally could.

The down side is that the thicker blood gives extra work to the pumping heart. This defence mechanism cannot of course operate against anaemia, when the fault itself lies in a deficient production of red blood cells.

The heart compensates for hypoxia by pumping out more blood per minute so that the actual delivery rate of oxygen to the tissues can be kept up despite its lower concentration in the blood.

These automatic attempts at self-preservation operate unless the lack of oxygen becomes too profound to sustain brain functions, including that of maintaining breathing itself. At worst, the heart weakens, the blood pressure falls, breathing stops, and cessation of the heartbeat soon follows.

Apart from "classical" Hypoxia, which is related to high altitudes and is almost an exclusive problem for mountaineers and, to a lesser extent, for air-travelling business men, Isobaric Hypoxia or simulated altitude, is also used for altitude training, a variety of sports endurance training as well as for fire prevention in a wide variety of applications which today include:

• Data Center, IT and Telecommunication environments;

• Electrical Switchgear

• Deep Freeze and other large Storage Facilities;

• Document and Artifact Archives;

• Chemical Warehousing;

As a consequence more and more people are being exposed to hypoxia.

Although there are some minor physiological differences between simulated (iso-

baric) and "real" altitude (hypobaric hypoxia), these are not relevant for occupational safety and health. Therefore the term "altitude" in this article includes the situation of "simulated altitude" (achieved by isobaric hypoxia) or "equivalent altitude" (a term, which is often used for aircraft cabin pressure).

Up to now there has been little or no consensus on how to provide occupational health and safety advice. Most regulations do not take into account the kind of exposure or specific circumstances related to Hypoxia, for example, whether a person is able to "escape" from hypoxia at any time, as is often the case under isobaric Hypoxia circumstances.

Regulations do not define the type or degree of different risks- if any - and therefore a more specialised analysis of the individual exposure is necessary to provide adequate advice for health and safety.

Facilities with isobaric Hypoxia can normally be left immediately and it is possible to maintain surveillance over persons working or exposed to Hypoxia, by persons not exposed to Hypoxia. This is a condition called "Controlled Hypoxia".

Personal risk is assumed to be much lower under "Controlled Hypoxia" than "Real Altitude" conditions where a person can neither escape from Hypoxia within a short time period, nor have his/her health condition under surveillance by a person that is not exposed to the same hypoxic conditions. This condition is called "Uncontrolled Hypoxia".

It is necessary to differentiate between the varying types of exposure to occupational Hypoxic conditions, and to establish the risk profile associated with each type of exposure.

To do this, the following five important factors must be taken into account:

• Altitude or equivalent altitude (% O₂), respectively

• Duration of exposure

• Altitude profile / acclimatization (including intermittent Hypoxia)

• Workload under Hypoxic conditions

• Native Highlanders versus Native Lowlanders

At least four kinds of exposure, each with its' own risk profile can be established considering the abovementioned five points:

• Extreme short exposure

• Limited exposure

These two profiles are subject to either no acclimatization or a short term acclimatization, such as is the case when flying, driving through a mountain pass, skiing, climbing or temporarily occupying an Hypoxic space where a fire prevention system exists.

• Expatriates

• Altitude populations

These two profiles are subject to adaptation to Hypoxic conditions for longer periods of time. This includes people who, at one time lived and worked at low altitudes but moved to live and work at high altitudes, as well as populations that evolved at high altitudes such as the Sherpas and Qetchuan.

This article will be continued in the next MenaInfra publication.

More information about Wagner in the Middle East can be found on our websites. For Fire & Life Safety Engineering Consultancy Services visit us at: www.wagnerfsmc.com

For Products and Fire Prevention Systems Engineering visit us at www.wagner-uk.com or www.wagner.de

Note: The Medical Commission of the Union Internationale des Associations d'Alpinisme (UIAA) is the world's umbrella organization for activity in low oxygen environments, coveting a special responsibility to coordinate an international consensus on this topic.