The Internet Encyclopedia (Volume 3)

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80 PHYSICALSECURITY

considerable and should be taken into account when plac-

ing the vents. The noise of a release is loud but not dam-

aging to hearing.

Gaseous fire-suppression systems can be either central-

ized or decentralized. In the former, a network of pipes

delivers the suppressant from a single tank to multiple

nozzles operating simultaneously; this is the more tradi-

tional and common approach. In the latter, independent

units each have a tank, triggering device, and nozzle; they

can be equipped for remote triggering or monitoring. Cen-

tralized systems are generally custom fitted for a partic-

ular installation. Decentralized systems are modular, so

there is greater flexibility in placing the individual units

or repositioning them (upon expert advice) if the layout

of a facility changes. On the negative side, the individ-

ual units, being self-contained, are heavier and bulkier

than the outlets and pipes of a centralized system. There-

fore, they must be supported from a structural ceiling

rather than a suspended ceiling. Moreover, each cylin-

der must be anchored very securely to prevent Newton’s

Third Law of Motion from turning it into a projectile upon

the release of gas. Gaseous agents that have been used

in computing facilities include carbon dioxide, argon, ni-

trogen, halogenated agents (halons), newer replacements

for halons, and mixtures of these. (Pure CO 2 at the con-

centration needed for total flooding is hazardous to hu-

mans.)

For decades, the fire-suppression technique of choice

in computing facilities was total flooding with Halon 1301

(bromotrifluoromethane or CBrF 3 ). (Halon 1211, a liquid

streaming agent, was also used in portable extinguishers.)

Because of their ozone-depleting nature, proportionally

worse than CFCs (chlorofluorocarbons), halons were

banned by the Montr ́eal Protocol of 1987. Disposal and

recycling of Halon 1301 must be performed by experts,

because it is contained under high pressure. Consult

Halon Recycling Corporation (HRC; 2002) for advice

and contacts. Although no new halons are being pro-

duced, existing systems may remain in place, and the use

of recycled Halon 1301 in new systems is still allowed

by the protocol (on a case-by-case basis) for “essential”

use (not synonymous with “critical” as used by the HRC).

Because the world’s supply has been decreasing since

1994, a concern when relying on Halon 1301 is its future

availability.

Halon 1301’s effectiveness is legendary. One factor is its

highthermal capacity(ability to absorb heat). More impor-

tant, it also appears to break the chemical chain reaction

of combustion. Although the mechanism by which it does

this is not perfectly understood (nor, for that matter, is the

chemistry of combustion), the dominant theory proposes

that the toxins into which it decomposes at about 482◦C

(900◦F) are essential for chemical inhibition.

In low-hazard environments, a concentration of ap-

proximately 5% Halon 1301 by volume suffices. Short-

term exposure at this level is considered safe but not

recommended for humans; dizziness and tingling may re-

sult. An even lower concentration is adequate when the

Halon 1301 is delivered with a dry chemical that inhibits

reignition. Regardless of the concentration applied, im-

mediately after exposure to Halon 1301 (perhaps from

an accidental discharge), a victim should not be given

adrenaline-like drugs because of possibly increased car-

diosensitivity. The real risk comes when fire decomposes

Halon 1301 into deadly hydrogen fluoride, hydrogen chlo-

ride, and free bromine. Fortunately, these gases, being ex-

tremely acrid, are easy to smell at concentrations of just

a few parts per million.

In addition to the natural inert gases, there are a numer-

ous replacements for Halon 1301 in the general category

of halocarbon agents. Subcategories include: hydroflu-

orocarbons (HFCs), hydrochlorofluorocarbons (HCFCs),

perfluorocarbons (PFCs and FCs), and fluoroiocarbons

(FICs). None of these or blends of them seem to be as ef-

fective, that is, more of the substance is needed to achieve

the same end. The search for better clean agents contin-

ues. See National Fire Protection Association (2000) for

guidelines regarding clean agents.

Water-Based Suppression

Despite its reputation for doing as much damage as fire,

water is coming back in favor. Because water’s corrosive

action (in the absence of other compounds) is slow, com-

puter equipment that has been sprinkled is not necessarily

damaged beyond repair. In fact, cleanup from water can

be much simpler and more successful than from other

agents. Water also has an outstanding thermal capacity.

Misting is now used as an alternative to Halon 1301. The

explosive expansion of the steam contributes to displac-

ing oxygen at the place where the water is being converted

to steam, namely, the fire. (Steam itself has been used as a

suppressant.) Pipes for hose, sprinkler, and mist systems

should remain dry until needed to reduce the risk of acci-

dental leakage.

First Response to Other Types of Incidents

One of the most likely incidents demanding an immediate

response is an unwanted intruder. In general, it is safer to

summon security personnel, particularly if the incident

warrants detaining the person for civil authorities. Less

likely but potentially more dangerous are incidents involv-

ing hazardous materials. It is possible to know in advance

precisely which ones are in nearby pipelines and storage

facilities, but not which ones pass by on transportation

arteries. Therefore, it is essential to know whom to call

should aHAZMAT(hazardous material) event occur or ap-

pear to be imminent. The safest course of action in case of

pipeline leaks, derailments, truck accidents, or deliberate

attacks is to evacuate immediately unless the substance is

known with certainty to be benign.

Because of the tremendous variety of characteris-

tics of modern contaminants, a facility contaminated by

chemical, biological, or radiological agents should not be

reentered until local authorities and appropriately trained

professionals give clearance. Some contaminants, such

as sarin gas, dissipate on their own. Some, such as the

anthrax spores, require weeks of specialized decontami-

nation. Others, such as radiation, effectively close down

an area indefinitely.

Disaster Recovery

Disaster recovery can take as many forms as the disasters

themselves. A single event may be handled in different