Sunday, December 19, 2010

Mercury Hangs Around



Photo Courtesy of
The National Atmospheric Release Advisory Center (NARAC)
 at Livermore Laboratory

*****


It doesn't take much in the way of common sense to know that dense gases hang low to the ground.  We've all seen gas dispersion models like the one above, etc., and we're all grateful to be able to use them.

However, there is something I'd like you to think about as it relates to gas releases and particularly to very dense gases.  What I'd like you to think about is the rate and pattern of mixing that occurs for such gases.  This is important when evaluating environments with flammable, oxidizing gases and/or toxic gases.  It is particularly important when we're planning for hazardous response strategies when we are dealing with mercury.

In general, two gases with molecular weight values close to each other will tend to mix more quickly than two gases where the molecular weight values are far apart.  For example, in a compressed gas cylinder (all other things being equal) I have found over the years that nitrogen and carbon monoxide will mix more quickly together than carbon dioxide and nitrogen.  There are, of course some limits on this generality- including the concentrations involved and the area of mixing interface.

The molecular weight of air is 28.996.  The molecular weight of mercury is 200.59.  Kind of a large differential, so even as it enters the air it's going to mix slowly.

Next, there's the vapor pressure.  Gases with liquid/vapor phases where the liquid has a high vapor phase such as carbon dioxide (830 PSIG), will enter gas phase quickly when released.  Mercery, on the other hand, has a vapor pressure of .0017 torr (not much of a vapor pressure at all, really) at 25 degrees C.  In other words, it will enter the vapor phase very slowly.  Other things being equal, heat will increase the vapor pressure.

The quicker the gas enters the vapor phase, the more quickly it will disperse unless there are outside factors working against it such as an inversion, the release occurring in a valley or in a confined space.  A hot day, of course, will accelerate this process.

Mercury, at normal temperature and pressure, will release slowly, continually over a long period of time, so it needs to be thought of differently than most of the dense gases.  There are similarities, of course, but the gasification of mercury, I think, is a little bit different animal than most.

Refrigerant gases have high molecular weights like mercury does, but they have higher vapor pressures.

So although we're used to thinking of dense gases (liquified gases shipped under their own vapor pressure) as somewhat similar, we need to give some serious thought whenwe're calculating the gasification of mercury because of its unusual combination of extraordinarily low vapor pressure and high molecular weight. 

I truly think it needs its own dispersion chart.

Wednesday, December 1, 2010

We Used to Play with this Stuff


We Just Do it a Little Differently Now

It looks a little like overkill, doesn't it? Some of us used to play with it as kids. But Mercury (Hg) is not a good toy.  Here's what JT Baker Chemical company says about it in their MSDS:

"DANGER! CORROSIVE. CAUSES BURNS TO SKIN, EYES, AND RESPIRATORY TRACT. MAY BE FATAL IF SWALLOWED OR INHALED. HARMFUL IF ABSORBED THROUGH SKIN. AFFECTS THE KIDNEYS AND CENTRAL NERVOUS SYSTEM. MAY CAUSE ALLERGIC SKIN REACTION."


What many don't understand is that Mercury is most dangerous in its gaseous state because concentrations of it can then be inhaled.  Or as JT Baker's MSDS says:

"Mercury vapor is highly toxic via this route. Causes severe respiratory tract damage. Symptoms include sore throat, coughing, pain, tightness in chest, breathing difficulties, shortness of breath, headache, muscle weakness, anorexia, gastrointestinal disturbance, ringing in the ear, liver changes, fever, bronchitis and pneumonitis. Can be absorbed through inhalation with symptoms similar to ingestion."

But it is still a underappreciated danger.

As far back as 1926, Alfred Stock of the Kaiser-Wilhem Chemistry Institute wrote:

"The insidious horror of mercury is not nearly sufficiently well known and is being taken note of too little in those places where one is particularly threatened by it, in chemical and physical laboratories."

And this is still true today.

Many emergency responders understand the dangers of contact with liquid mercury, but do not yet understand that 1) mercury readily vaporizes, and that 2) it is a terrible danger in the gas state.  Many teams do not have readily available vaporized mercury detectors. 

Three companies that I know of  make fine mercury vapor detectors: Arizona Instruments, Lumex of Ohio, and Ion Sciences.

An article from MedicalNewsToday back in 2004 reported:

"All mercury spills, regardless of quantity, should be treated seriously. Metallic mercury slowly evaporates when exposed to the air. The air in a room can reach contamination levels just from the mercury in a broken thermometer - just a few drops.

When liquid mercury is spilled, it forms droplets that can accumulate in the tiniest of spaces and then emit vapors. Health problems caused by mercury depend on how much has entered your body, how it entered your body, how long you have been exposed to it, and how your body responds to it."



Mercury may be the densest liquid known, but it still has a vapor pressure of .2729 mmHg, which is still sufficient for it to vaporize into the air to the level that it can harm you.  Like all liquids with a vapor head, the quantity of gaesous fumes that enter the air is temperature dependent.  So the hotter the day, the faster the gasification occurs.

More on this next week.

Monday, November 22, 2010

Distant Measurement and Responder Psychology- Part Three of Three


How Close Would You Like to Be to This?


Responders need to reduce unnecessary job stress so they can think clearly during the performance of their already stressful jobs. Training is critical toward that end, of course, and so is having the right equipment. These two concerns are discussed a lot in the industry. But today I'd like to deal with an issue that is too seldom discussed, and that is the distance factor in hazards detection and its effect on a responder's psychology.

In general, the further removed we are from physical danger, the more clearly we are able to think about the issues involved. Sound too vague? Let me give you a specific.

You're approaching a rail car where you suspect that a polymerization reaction might be occurring. One way to see if that is going on is with an infrared temperature gun. With most of today's IR guns, you have to get uncomfortably close to see if an exothermic reaction is in progress. That's because the aspect ratio of most guns is 50 or 65:1. Also, their laser targeting dots are difficult to see in daylight, so you have to get close enough to see that they are on what you're aiming at. Having to get close to a potential hazard before you can tell how bad it is makes for a serious stress multiplier.

After the folks at Hazmat IQ alerted me to this situation, I went to work with a few researchers to develop an IR temperature gun that has a 100:1 aspect ratio, and uses two DayBrite laser (Class III laser) targeting dots that are much, much easier to see from a distance in daylight.

What I noticed in discussing this new product with various responders was the obvious relief they experienced. Obviously, they could use this new IR gun from a greater distance and would therefore be safer, but I think that the other benefit is in the impact on responder psychology.

Here's what I'm thinking- the greater the distance from a potential safety hazard that a responder knows what's going on, the more time they have to clear their mind and concentrate on other issues. Knowing what's going on as earlier as possible reduces the stress of not knowing and we can think more clearly.

When I hear responders say they think more clearly under stress, I know they don't understand responder psychology. Stress might get us on edge, but it doesn't make for clear thinking. And the earlier we know about potential dangers, the better chance we have to calm down and make good decisions.

Sunday, November 14, 2010

Confined Spaces and Responder Psychology- Part Two of Three

- P


Maintenance Workers and Contractors
Are Not the Only Ones
Who Should be Afraid of Confined Spaces


*****


Confined spaces are dangerous for maintenance workers and contracters.  That's why a Michigan Company called Bharat Forge America out of Lansing was fined $126,000 for confined space entry violations.  OSHA has very specific strictures regarding the gas detection equipment required to enter confined spaces.  They don't take kindly to people who are not properly outfitted for gas detection.  But a group of contractors that I was training last week tipped me to another hazard- anxiety attacks and the confused thinking that results from them.

Estimates vary, but most psychologists are comfortable with assessments that 5-10% of the world's population suffers from claustrophia.  Claustrophobia is essentially a fear of being trapped in a confined space. 

What the construction workers pointed out to me was that even with proper safety equipment, the anxiety some of them experienced made it occasionally difficult to properly use that equipment.  Although I was at first skeptical, as they continued to talk about the effects of claustrophobic feelings (constant dread of suffocation and the need to flee), I remembered a worker I've mentioned before who when faced with an emergency ran roughly a quarter mile to ask a co-worker the phone number for 911.

Later, I spoke to other people who have entered confined spaces in emergency scenarios that required portable gas detectors.  One confessed to having been in such dread of entering a sewer emitting an awful smell that he forgot to turn the detector on.

That's a recipe for disaster.

The ability to process information is diminshed.  Memory and training can be clouded for even the most experienced responder.  There is an inability to focus.  Not the proper mindset for a responder.
Have you had experiences with this particular issue?  Have you ever thought about the effects of Confined Space Entry on the psychology and functionality of yourself or your team?  Do you routinely screen your responders for claustrophobia? 

It's worth thinking about.

Sunday, November 7, 2010

Hazardous Gas Releases and Responder Psychology- Part One of Three



Gases are Risky Business

There are a number of reasons why hazardous gas scenarios are among the most psychologically difficult of all hazmat situations (other variables as equal as we can get them).  And the psychological state of a responder is just as important as their equipment.

First, many- in fact most- gases are invisible.  Without the use of proper gas detection (and that always has a few variables), a hazmat responder is walking in blind to these situations.  And this was a factor when I dealt with emergency situations with flammable or toxic gas.  Even oxidizers and inert gases- when I was young and naive I used to think of these as "safe" gases- can affect our psychological state.  There's just something about facing off with an "invisible enemy."

A friend of mine who served in Vietnam described how difficult it was to be plagued by guerilla attacks from Viet Cong who seemed to appear from nowhere, attack and then disappear again.  This before he and many others came to grip with the tunnel systems in use.  In fact, he told me that the psychological damage they infected was worse than the actual physical damage.

When gases leak, they disperses to cover a wide area.  So, when I was in such a situation, in my mind I used to feel "surrounded" by invisible hazards.  If it was a flammable gas, where would the spark come from that would cause my last day on earth?  If it was a heavy oxidizing gas, as it dispersed would it come in contact with grease or a fuel source?

So, the first two challenges a responder has to deal with in regard to gas hazards are that most times the gas is invisible, and that it disperses quickly so that the responder will literally and mentally be "surrounded" quickly.