Hot work permit without a gas test!

For more information about Gas Monitors, please download the Gas Monitors Training Course

Recently the US Chemical Safety Board released a video animation of the sequence of events at a DuPont facility near Buffalo,NY that had an accident due to hot work being carried out on a storage tank that still had explosive vapors. Surprisingly the workers who carried out the hot work were issued a mandatory "hot work" permit WITHOUT carrying out any gas test ! (A gas test is a test that is carried out to ascertain the presence of an explosive gas before allowing hot work such as welding or cutting inside a plant).This negligence unfortunately caused the accident. It could have been easily prevented had a Gas Monitor been used.

The CSB has posted an animated video that details the incident. watch it below.

Confined Space Gas Monitors- Some basic facts

For more information about Confined Space Gas Monitors, please download the Gas Monitors training course. It will help you understand all about gas monitors including Confined Space Gas Monitors

What is a confined space gas monitor?
A confined space gas monitor is an instrument that allows people to enter and work safely in confined spaces. These confined spaces are commonly found in the process industries. For example a worker who enters an empty petroleum storage tank, is entering a confined space. These confined spaces may have several hazards and a confined space gas monitor helps in reducing these hazards.

Why use one?
For starters, using a confined space gas monitor is absolutely essential to save lives of people who work in such confined spaces. Also by law it is compulsory to use certain protective equipment while working in confined spaces and one of these equipment is a gas monitor.

What does a confined space gas monitor have?
A confined space gas monitor, is any portable kind of gas monitor that can sense at least two gases- Oxygen and Explosive gas. More the gases detected, obviously the better. Also if the confined space is normally used to store or process toxic gases (like Chlorine) then this gas monitor must also include the toxic gas sensor (in this example it would be a Chlorine sensor).
There is an excellent article on basics of toxic gas detectors that you can read here).
Thus a typical 4 gas detector that has one of the sensors as oxygen, can be used as a confined space gas monitor.
The monitor must in addition be lightweight, shock and fall proof, explosion protected (if used in a hazardous area), be small enough to be carried by a worker in his pocket or on a belt clip and have an easily visible display and a loud enough hooter/buzzer.
Some newer ones may also feature a wireless communication to the control room that transmits the readings continuously as well as alarms the control room operators in case of high/low levels of the gases detected.

Calibration
The monitor must be capable of being calibrated easily with calibration gases on site. Further the plant engineer should ensure that at least bump tests of these instruments are regularly done, if not full cycle calibrations, to ensure that these instruments continue to work as desired.

That's all!
For a detailed training course on confined spaces, have a look at the course below

Four gas monitor or PID meter? Which one do you use?

For more information about Gas Monitors, please download the Gas Monitors Training Course

Many people in the process industry used to use a standard "four gas" monitor for years, until the advent of PID type gas monitors. So this is just an open ended question to you all... what's your favorite meter? To the newbies, a four gas monitor is basically what it says, a portable gas monitor that can measure upto four different types of gases. These can be any mix of four sensors, or a mix of one LEL sensor (for explosive gases and vapors), an Oxygen sensor (for confined space entry) and two toxic gas sensors (say H2S and Chlorine for example). These type of four gas monitors have been used for several years and are workhorses of the plant operations and maintenance teams. However the advent of PID type meters has meant a threat to the domination of the four gas monitor. Essentially a PID meter stands for a gas monitor that uses a PID (Photoionization detector) to measure a wide range of gases. These cover most compounds found in industry such as most volatile organics and toxic gases like H2S. Many PID meters also come with a built in software and systems to automatically do datalogging and calculations of parameters like TWA, etc for regulatory compliance. Calibration is easier too, with just one gas IsoButylene being used.
So tell us what's your favorite meter- PID or four-gas?

How to verify if a gas monitor is really working?

For more information about Gas Monitors, please download the Gas Monitors Training Course

As you all know the reliability and accuracy of an instrument can only be verified after it is calibrated against a known standard. This is also the case with toxic gas monitors as well as other types of gas detectors.

In case of gas monitors, there are two ways to check the functioning, one is a full fledged calibration where the sensor is exposed to different concentrations of a known air-gas mixture (to calibrate it at various points from minimum to maximum) and the other is to subject it to a "bump" test. A bump test exposes the sensor to just one known concentration of the gas, to verify if it responds.

Now which amongst these two methods should you use?

There are two issues here. First, are you interested in the accuracy of measurement, or merely the functional testing? Accuracy of measurement is important in many applications, where, for example, an oxygen meter is used for confined space entry. A reading that shows 20% when the actual value is say 17% can be disastrous. Here, we require that the instrument always function at it's best accuracy and has to be thoroughly calibrated always. Also a "bump" test is simple, just check the reading in the outside air-it should Oxygen of about 21% (more or less depending on the area and the pollution levels).

However in other cases, the instrument may be used more for detecting the presence of a toxic gas rather than its exact concentration. Suppose a Chlorine gas monitor is installed on the outlet of a vent line, that carries away vent gas away from a confined Chlorine storage area-here the presence of Chlorine must be detected, rather than the exact ppm level. It does not matter whether it shows 2 ppm when the level was 1 ppm. It has to detect the presence (according to its minimum resolution). Here, instead of subjecting the Chlorine gas monitor to a full calibration, it may be simpler to bump test it once a while. As long as it responds to a bump test of the lowest concentration of Chlorine, it's fine, you need not carry out a full fledged 3 or 4 point calibration.

What are the advantages of bump testing?
1. It is simpler than a full fledged calibration
2. Less lecetrolyte is consumed in case of electrochemical sensors-this increases the life of the sensor substantially
3. Cheaper and easier-just one gas bottle per type of gas is needed.

Any other advantages? Please use the comments section below to post.