Fire extinguishers basics

What is fire? We’ve all seen fire. Probably felt it too. Fire is the rapid oxidation of a material  – a process known as combustion. It is exothermic, therefore it releases heat. We also know it produces light. Lastly, we know it burns or vaporizes things.

fire extinguishingMechanism of fire onset:

Fire is nothing without its three components – oxidizing agent, heat and fuel. The visible part of fire is called the flame. In my previous post, I mentioned how the fascination towards colorful flames caused a severe accident. Anyway, we’ll get to the safety aspects in a while. So, fire only comes into existence when there is enough oxidizing agent (mostly oxygen), enough heat and enough fuel. When I say ‘enough’, I am trying to quantify it. What I mean is, if one of these three components is in less supply, there won’t be any fire. It also means that as long as these three components are in sufficient supply, the chain reaction that causes fire will continue and the fire will not go away.

Why do we need to extinguish fire?

We know that fire can cause loss of life, loss of property and environmental destruction. To know how fire extinguishers work therefore comes handy. For those who do not know what fire extinguishers are – fire extinguishers are red cylinders containing a certain fire extinguishing chemical inside it. In simple terms, these are devices that can contain small fires.

How do fire extinguishers work?

Fire extinguishers smother fire by:

  • keeping oxidizing agent from reaching it
  • replacing the oxidizing agent with an inert gas
  • preventing the chain reaction (chemical reaction) that’s causing the fire to sustain itself
  • absorbing the heat from the burning material

Fire extinguishing materials:

The most common and probably the most easily available fire extinguisher is water. But beware, it doesn’t work in all cases. It won’t work if the fire is caused due to, say, electronic short-circuit. It can therefore do more damage than good. OSHA (Occupational Safety and Health Administration) provides a list of common fire extinguishing materials and here they are:

The last two types were discontinued from use when the Montreal protocol came into effect. This is because when the two chemicals decompose, they decompose into bromine and chlorine, which then mess with the ozone layer.

Fire classes:

The tricky part of all this is knowing which fire extinguisher to use for which type of fire. Yes, there are types of fire and they are categorized into a number of different fire classes.

  • Class A: Ordinary combustibles
  • Class B: Flammable liquid and gas
  • Class C: Electrical
  • Class D: Metal
  • Class K OR Class F: Cooking oils and fats (kitchen fires)

Fire classes can vary a bit according to the country you reside in. So, it is important that you first find out information specific to your own country. For example, in the UK, class B is further divided into two parts: one for liquids and another class C for gases.

Fire training:

Most laboratory and industry personnel have basic or rigorous training in fire fighting. For those who don’t have any access to such training, Wikihow can help, but only so much. You really have to get some practical knowledge – a single demonstration can someday help you save yourself or others. May be a friend from a fire fighting department can help you give a demo or one can request them to have such sessions for your entire community. Training – no training, fret not. Here’s something you can do yourself. Get to your nearest fire extinguisher, you probably know how it looks like. All you have to do now is to read what is written on it. Click here to read about how you can read the details on the cylinder and what it means in simple English. Next, go to YouTube and find videos which demonstrate how to use a fire extinguisher. Something like this video:

Further reading:

What chemicals are used in a fire extinguisher? How do they work to put out fires? – Scientific American

Enjoy the song. ;)

Safety during ultrasonication

James Bond in Casino Royale shoots a propane tank with a handgun. You didn’t miss that did you? If you did, do you at least remember what happens when a gas tank explodes after a crash in Terminator 2: Judgment Day? It’s okay if you don’t, because I’m going to tell  you what happened when the famous ‘rainbow experiment’ went wrong in a lab. Not once but twice.

Chemicals are as nasty as they are shown in films. Chemicals are also very noxious in a chemical laboratory as much as they are at any place else. That’s why wherever you are, whatever you do, chemicals should be handled with care. (Girls, even the acetone that you use to remove nail polish from your nails can catch fire as soon as it comes in touch with an ignition source, i.e. fire.)

Coming to the rainbow experiment. It’s really fascinating to look at. What happens is, when elements such as Na, Sr, K, Li and Cu are mixed with methanol and ignited, they all burn in the colors of a rainbow. You can see its video here.

What went wrong with the rainbow experiment?

A teacher’s chemistry experiment exploded during a demonstration at Beacon High School in Manhattan on Thursday, creating a fireball that burned two 10th graders, one severely, according to Fire Department and school officials. – Chemjobber

It is better to be safe than sorry. As you can see, horrible things have happened, not only to grown-ups but also to children. This doesn’t meant you should avoid doing things that involve risks. Instead, you can do it in a safe way.

As students who had to work in a laboratory, we were told by our professor (Prof. Bhujle) to learn the safety aspects of our respective projects. For those who do not know me or what I was up to during my Masters degree, here’s what I did:

Process intensification using alternative energy source i.e. ultrasound irradiation (sonochemistry), which leads to decrease in energy consumption and waste reduction. Also investigated a Lewis acid catalyzed homogeneous organic condensation reaction and an ultrasound-assisted Pd-catalyzed heterogeneous transfer hydrogenation reaction.

Safety aspects associated with the project:

Ultrasound usage can be categorized as:

  • Low frequency, high power ultrasound (20–100 kHz)
  • High frequency, medium power ultrasound (100 kHz–1 MHz)
  • High frequency, low power ultrasound (1–10 MHz)

The equipment I used to generate ultrasound i.e. ultrasonic bath, runs on a 33 kHz frequency. Hence, it can be taken as low frequency, high power ultrasound.

Contact Exposures:

Contact exposure is exposure for which there is no intervening air gap between the transducer and the tissue. This may be via direct and intimate contact between the transducer and the tissue or it may be mediated by a solid or liquid. Contact exposure can in some cases provide nearly 100% energy transfer to tissue. [1] 33 kHz frequency ultrasonic bath can cause observable effects.

Airborne ultrasound:

The most plausible mechanisms for non-auditory effects of airborne ultrasound on a human are heating and cavitation. [1] An exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). [2] The major effects of airborne ultrasound of concern in practice are the result of reception by the ear. To summarize, exposure to ultrasonic radiation, when sufficiently intense, appears to result in a syndrome involving manifestations of nausea, headache, tinnitus, pain, dizziness, and fatigue. The type of symptom and the degree of severity appear to vary depending upon the actual spectrum of the ultrasonic radiation and the individual susceptibility of the exposed persons, particularly their hearing acuity at high frequencies. A concise summary of the physiological effects of ultrasound with specific stated exposure conditions has been given by Acton.

Measures to be taken for safety:

  • Contact exposure to high-power ultrasound must be avoided at all times. [1]
  • Only operators qualified to use the equipment or persons under strict supervision should be allowed within the boundaries of the controlled area while the equipment is operating. [1]
  • Personnel using high-power ultrasound, and safety inspectors in industry should be knowledgeable about the possible harmful effects of ultrasound and necessary protective measures. [1]
  • Warning signs should be placed at the entrance to any area which contains high power ultrasound equipment or applied to each high power ultrasound device. Accompanying each warning sign there should also be a statement indicating the precautionary measures to be taken while the ultrasound power is on. [1]
  • Safety procedures for the protection of personnel are similar to those used for audible noise. The protection for ultrasonic frequencies is expected to be at least 14 dB for ear muffs and rubber ear plugs, and 24 dB for foam ear plugs. [1]

1. Guidelines for the Safe Use of Ultrasound Part II – Industrial & Commercial
Applications – Safety Code 24. Health Canada. ISBN 0-660-13741-0, (1991).
2. AGNIR (2010). Health Effects of Exposure to Ultrasound and Infrasound. Health
Protection Agency, UK, 167–170.

I’ll discuss transfer hydrogenation in subsequent blog posts.

Stay safe. ;)