Tag Archives: respirator

Smell is Irrelevant

“This doesn’t smell bad so I don’t need a respirator.” I hear that from time to time, either from students or in online forums. Prop makers working with chemicals use their sense of smell to determine how dangerous something is. “This smells better than that, so I don’t use that anymore.” “I can’t smell a thing, so this must be safe.”

No no no. This is dangerous, and the wrong way to think about safety with chemicals.

For every chemical, OSHA sets limits as to how much you can be exposed to. They try to figure out the amount you can be exposed to while working with something your entire life, and never have adverse health effects from it. These are called Threshold Limit Values (TLV).

The first is  the time-weighted average (TWA). The TWA is meant to indicate what you are constantly exposed to at work. They measure the average amount you are exposed to over an 8-hour day and a 40 hour week. (Uh oh, we often work much more than that in theatre).

Next is the short-term exposure. or STEL. They define this as 15 minutes of exposure. And you have to have an hour break before the next exposure. And you can only have four exposures per day.

Finally there is the ceiling value. You should never reach this level of exposure, even for an instant. They also have IDLH, which is “immediately dangerous to life and health”. Instant exposure at this amount will kill or irreversibly affect your health.

So let’s look at the following chart, which has the TLVs for some common chemicals found in the props shop. You probably recognize some of these as ingredients in paints and coatings. Amines are found in many epoxies. Methyl ethyl ketone is used in polyester resin. The diisocyanates (TDI and MDI) are two of the more common curing agents used in two-part polyurethanes.

All the values are measured in parts per million (ppm), which means out of a million pieces of air, that is how many pieces are of the substance being measured (for comparison, room air has 209,500 ppm of oxygen).

Odor thresholds and Threshold Limit Values of certain chemicals

So where does smell come in? Well, every chemical has an “odor threshold”. This is the amount, again in ppm, of a chemical at which point you can smell it. This is much less standardized, because it can be hard to test and different people have different sensitivities to smell. The number is often given in a range. You can see in the chart that the odor thresholds are all over the place for the different chemicals.

I’ve pulled a few chemicals out and put them in a chart so you can see what’s happening a bit easier.

 

Chart for OT and TLV

Look at chlorine. The odor threshold is way below the TLV TWA. This means that even if you smell chlorine, you may not be exposed to a harmful amount. You may be able to smell chlorine all day every day and still not have harmful effects (like if you work at an indoor pool).

Now look at formaldehyde. The short-term exposure limit (the orange dot) is way down in the graph. The odor threshold is way at the top. That means you can be exposed to a harmful amount before smelling it. In fact, you will have to be exposed to three times the threshold limit before you can smell it. So if you are working with something that off-gasses formaldehyde (including many plywoods and engineered lumber, VOC-containing paints, and even some fabrics), you cannot assume you are safe because you do not smell anything.

Look at the two diisocyanates (MDI and TDI). Both of them also have an odor threshold above their short-term exposure limit. If you look back at the chart, you will see that the STEL for MDI is also its ceiling value, which is the amount you should not exceed even for an instant. And its odor threshold is twenty times higher than that. You can be breathing dangerous and even deadly amounts of MDI before you even get close to smelling it.

This is why many people suggest casting urethane parts inside a fume hood or a spray booth; even a respirator is not a reliable protector. One way to tell if your respirator has stopped working is if you can smell the outside air. But with these chemicals, you cannot smell them even when they are present in dangerous amounts. So you have no indication of whether your respirator is working or not.

Your nose is a great sensor for many chemicals, but you should never rely solely on it for your safety. You need to know about the specific chemicals you are working with and how their odor threshold relates to their threshold limit values. No more, “this doesn’t smell bad so I don’t need a respirator.”

Smell you later.

N95 Day

A little over a week ago was N95 Day, a day which NIOSH created four years ago to raise awareness for respirator-use in the workplace. It happens every September 5th – get it? N95 = 9/5 (in the US, we put the month before the day. Sorry, rest of the world).

The N95 is the most common type of respirator used in the workplace, and is probably the most common found in your props shop.

"Fit Testing the N95 Mask" by AlamosaCounty PublicHealth is licensed under CC BY 2.0
Fit Testing the N95 Mask” by AlamosaCounty PublicHealth is licensed under CC BY 2.0

Some people think the N95 is a dust mask, not a respirator, but that is incorrect. The N95 is a disposable particulate respirator, but it is still a respirator, so all the rules and requirements for wearing a respirator must be followed for the N95 as well.

A couple of things about respirators. First, you have to know when to wear the right one. If you have The Health and Safety Guide for Film, TV, and Theater, or if you have ever attended a workshop by Monona Rossol, you know that airborne hazards come in five flavors: dust, mist, fume, vapor and gas. Dust, mist and fumes are particulates, which means they are bigger than air molecules and can be filtered mechanically. Vapors and gasses are the same size as air, so you can’t just block them; you need to chemically absorb them. So an N95 can stop dust, mist and fumes, but you need a classic cartridge respirator to stop vapor and gas.

You really need to know what you are dealing with to pick the right respirator. Using contact cement produces hazardous vapors, so an N95 will do absolutely nothing. In fact, some may argue that since any respirator creates extra stress on your body, wearing the wrong type of respirator can actually be worse than wearing no respirator.

Most chemicals we use have a mix of hazards. Spray paint is a prime example; the paint comes out in a mist, but the solvents produce vapors. So you need both a particulate and a chemical respirator. Most of the cartridges you can get for your respirator have a combination filter for doing both.

One final note: you often come across shops where they are really gung-ho about eye and tool safety, but cavalier about using respirators. It’s true that if you lose an eye, it sucks, but you have two eyes, and you can still live without being able to see. A respirator protects your lungs, and if you can’t use your lungs, you’ve only got about three minutes of life left.

Captain Cutie
Captain Cutie

This is my son. He’s adorable, right? He’s lived in the hospital since he was born 14 months ago, and needs to be hooked up to a ventilator 24 hours a day to breathe. His lungs are too small to support him. Most of us take our lungs for granted and don’t stop to think that every breath we take is a small miracle.

Not being able to breathe sucks. Wear your damn respirator.

The Nose Knows Not

I often see a lot of products advertise themselves as “low odor”. I also hear the occasional prop maker mention that one product is safer because it “smells better” than an alternative.

What is smell? Smell means you are detecting airborne particles, fumes, gases, vapors, dusts and mists. And if these tiny airborne things are reaching your nose, than you can be sure some of them are entering your lungs, and from there, your bloodstream. So smelling something is a warning that you may be breathing hazardous substances.

But the smell is not related to the toxicity of that substance. In fact, particularly odorous substances can, in some situations, be safer than their low-odor counterparts. Relying on your sense of smell is a poor method of determining the quality of the air you are breathing and whether you should be wearing a respirator or working in a spray booth. Let’s see why.

First, a brief foray into the world of measuring toxic exposure amounts, as well as how we measure “smell”. You need the MSDS to know what chemicals are in the products you are using and in what quantities.

OSHA measures the amount of a substance in the air using “parts per million”, or PPM. For example, if Chemical X is recorded at 1000 PPM, than for every million atoms of air in a room, one thousand of those are Chemical X. The other 999,000 are probably atoms of oxygen, nitrogen, carbon dioxide, water vapor and so forth.

To determine the safe level that certain chemicals can be worked at without causing harm, OSHA has a number of measurements related to the threshold limit value (TLV). The TLV gives a number in PPM; above that number is harmful, below is not. The TLV is indicated in a number of ways. There is the “ceiling value”, or TLV-C, which is the amount that should never be exceeded. The TLV-C is usually pretty high, because it takes a lot of any single chemical to harm you in one breath. More common is the time-weighted average (TLV-TWA). This gives you the average level of a chemical exposure over a period of time (usually eight hours unless otherwise indicated). 1 This number is far lower than the TLV-C, because you are being continuously exposed to a certain level over an extended time. 2

Let’s look at acetone. Acetone has a TLV-TWA of 500 ppm. That means that over an eight hour day, your body has been harmed in some way if you have breathed, on average, 500 molecules of acetone with every million pieces of air. It may be higher at times—such as when you open a can of acetone—and lower at other times, such as when it has all evaporated and you are working on something else.

Getting back to smell, the other important measurement is the Odor Threshold (OT). This measurement, also in PPM, indicates at what concentration you can smell that particular chemical. Acetone has an OT of 62 PPM.

Let’s see what happens. You are in your shop working with acetone. It fills the air at 30 PPM. You keep working with it. It is now 62 PPM; you start to get a whiff of that distinctive acetone smell. “Uh oh.” you think. “Better open a window and set some fans up.” The increased ventilation brings the concentration of acetone back down to 50 PPM. You no longer smell it. During this whole time, your exposure to acetone never even gets close to 500 PPM because the smell alerts you to the fact that you are being exposed; you smell it in a concentration far below what is dangerous to breath.

Now let us look at another chemical common in the props shop. Hexane (or n-hexane) is used as a solvent, and is found in some cleaners and degreasers, as well as in adhesives, particularly fast-drying glues or cements intended for leather. Hexane has  a TLV-TWA of 50 PPM and an OT of 130 PPM.

Let’s step through another typical day. It’s the morning and you are gluing some leather together. Your exposure to hexane creeps up to 80 PPM for a few minutes. You clean something off with a hexane-containing cleaner and the concentration of hexane goes up to 100 PPM. You work on something else for a few hours and the level of hexane drops to 10 PPM as it evaporates. In the afternoon, you are using some rubber cement and white-out (both of which typically contain hexane) and your exposure goes back up to 60 PPM. In fact, by the end of the day, your average exposure (your TLV-TWA) has been around 55 PPM—above the limit of 50 PPM, meaning you inhaled a harmful amount. However, the level never even approached the OT of 130 PPM, so you never smelled it.

In other words, if you relied on your sense of smell to warn you of dangerous chemical exposure, it would have failed you in this case.

Any chemical with an OT above its TLV-TWA will not warn you with its scent before you are exposed to dangerous levels. Some chemicals lack any adequate warning signs for overexposure. The cyanates used in polyurethanes popularly used in molding and casting are particularly egregious. For instance, Methylene diphenyl diisocyanate (MDI) is commonly found in two-part rigid polyurethanes and polyurethane foam. Though one of the least toxic of the isocyanates, it still causes harm at low levels 3. Exposure can also create sensitization or allergies, which leads to violent or even fatal reactions in workers exposed to even a small amount. The TWA is only 0.005 PPM (the PEL is actually 0.02 PPM, but that is a ceiling limit). The OT has not even been established, but you can be expected to have some warning in the form of eye and nose irritation around 0.05 to 0.1 PPM. 4 In other words, you may not have any warning until you have been exposed to at least ten times over the amount that is safe to breathe over eight hours, or even five times the maximum amount you should breathe at any one time. Even then, you may not correlate your runny nose or watery eyes to the polyurethane; it has no distinctive smell, so you may just continue on, thinking “Hey, this is great. It doesn’t smell bad, so it must be safe to breathe.”

That’s wrong. Dead wrong.

Notes:

  1. You will also run across the PEL (Permissible Exposure Limit) of a chemical. This is the actual legal limit established by OSHA, above which an employer cannot expose its workers to. You have to check what the PEL is measure in; a TLV-TWA for eight hours is often used, but it may also a shorter exposure time or even a ceiling limit.
  2. Many other organizations have their own standards and measurements, and not every chemical has been measured in every way. So acetone has a TLV-TWA of 500 PPM, but the TLV-C has not been established by OSHA. It does, however have an IDLH (Immediately Dangerous to Life or Health) of 2500 PPM; this is typically a bit stronger than TLV-C, indicating you can probably die with a short exposure (under 30 minutes) at this level.
  3. See this compilation of health hazards of MDI.
  4. Occupational Health Guideline for Methylene Bisphenyl Isocyanate (MDI), US Dept of Health and Human Services, 1978.

Celastic

 

What is Celastic?

Celastic advertisement
originally uploaded by Trimper's Haunted House Online

Celastic was first trademarked in 1926. It was being used by the theatrical industry as early as the 1930s, and saw its most widespread use in theatres of all sizes by the 1950s. It appears to be one of the most popular prop-making materials of the ’70s and ’80s, and why not? It was used to make everything from masks to armor, statues to helmets. It reinforced other props, or simply gave them a smooth, flowing surface.

Celastic is a plastic-impregnated fabric which is softened with a solvent such as acetone or MEK. When it is soft, it can be manipulated into nearly any shape; it can be wrapped around forms, pushed into molds, or draped over statutes. You can cut it into strips or small pieces; Celastic adheres to itself. When it dries, it becomes hard again, thus retaining whatever shape you can manipulate it into. If necessary, it can be resoftened and further manipulated.

Here is an example of what passed for safety knowledge back when the use of Celastic was prevalent: “Rubber gloves should be used to keep the Softener off the hands. The liquid is not injurious under normal working conditions… Common-sense precautions will make the medium acceptable for any school use” (Here’s How by Herbert V. Hake, 1958). Of course, “not injurious” is not the same as “harmless”.

Acetone and MEK of course can be absorbed through the skin, and the fumes can cause neurological damage. As prop makers became more health-conscious and aware of the effects that cumulative exposure to solvents, especially strong ones like MEK, could have on their bodies, they began seeking out alternatives and scaling back the use of Celastic. Today, you’d be hard-pressed to find even a single practitioner using this material. You find one occasionally; their argument is that no other material can be draped as finely as Celastic, and if you take the proper precautions, you can protect yourself. There is some point to that; all chemicals can harm your body to some extent, and you need to be aware of how that chemical can enter your body, how much is entering it, and how to properly limit your exposure to it. If you wear the proper gloves and sleeves, respirator, goggles and face shield, and work with the solvents in a well-ventilated area (preferably some kind of spray booth or hood), working with Celastic would be no more dangerous than working with wood.

Of course, we rarely work alone in theatre; if one person is working with Celastic, than everyone is breathing the fumes. Prop shops are rarely the best ventilated areas, so the vapors can hang around long after everyone has removed their respirators. And of course with all the deadlines and time pressures, the temptation to take shortcuts in safety are always present; “I’ll just dip this one piece in Celastic really quickly; I don’t need to go all the way to my locker to get my respirator.”

Most prop shops these days seek to use the “least toxic alternative.” Whatever perceived benefits Celastic may have is far outweighed by the existence of less toxic materials that will accomplish the same goals.

Some of these alternatives are thermoform plastics which are softened by mild heat; they can be dipped in boiling water or blown with a hot air gun. One of the first to be introduced was known as Hexcelite; it was developed as an alternative to plaster for setting broken bones in a cast. Today, it is sold under the trade name of Varaform. Two other popular brands are Wonderflex and Fosshape. Wonderflex is a hard plastic sheet, while Fosshape is more of a plastic-impregnated fabric.

Breathe Nothing But Air

A visual comparison of healthy versus harmful gases.
A visual comparison of healthy versus harmful gases.

My father is a potter, and his job includes all sorts of dangers to the lungs, such as dust from dry clay, mist from spraying glazes, and fumes from firing pots. His words of wisdom for dealing with all this safely are “breathe nothing but air.” Putting these simple words into practice can be a bit more complicated, however.

Proper ventilation is a must when working in almost every aspect of prop-making: wood-working, welding, molding and casting, painting, etc. You can (and should) supplement it with more specific safety measures, such as respirators and dust collection systems, when necessary, but overall ventilation is still the backbone of any healthy prop shop. Without ventilation, you will be putting other workers and visitors to your shop at risk. Also, many harmful particles remain in the air for a long period of time, well after you’ve completed your task and removed your respirator.

It’s helpful to know the different kinds of harmful substances that may enter your lungs, as this will determine what kind of protection you need. I learned about the various physical forms a chemical can take while working at the Santa Fe Opera, which has a great safety training program:

Solid, liquid, fume, dust, mist, gas, vapor.

I would hope you know what a solid and a liquid are; the other forms may require some explanation. It is important to know the difference between them because they determine what kind of protection you need to keep them out of your lungs. Wearing a dust mask to protect against vapors, such as those found in spray paint, is not only useless, but can even be more harmful than wearing nothing. Why? When wearing any kind of mask or respirator, your lungs need to work harder to pull in enough air to breathe, so wearing the wrong kind of mask will make your lungs suck in more spray paint than when your breathing rate is lower.

When a solid is heated to its melting point, it may release a fume, which is a solid particle suspended in the air. Welding and soldering are common practices which create fumes.

Sanding, grinding and even just handling powders can create dust. Like fumes, these are solid particles floating in the air. Though most dust is trapped by your nose hairs, some dust is so fine it can make it all the way to your lungs; these are known as “respirable” dusts, and are the most harmful. Some are so fine they are invisible.

Tiny liquid droplets in the air are known as a mist. You can create mists from spraying liquid, or from boiling it. Some mists may even carry solid particles inside.

A gas is the third phase of matter, after solid and liquid. Normally, when we talk about what form a certain material comes in, we talk about what phase it is at room temperature. Common gases used in the props shop can include argon and carbon dioxide for welding, and acetylene and propane for torches.

When a liquid evaporates, it becomes a vapor (notice how “vapor” appears in the word “evaporate”). Evaporation can be sped up by heat. Vapors are molecules just like gases, and the only real difference between the two are that vapors can re-condense to a liquid or solid in a high enough concentration.

You’ll notice the first three forms–fume, dust and mist–are all particles of some sort. You can filter particles with a physical barrier, such as those found in NIOSH-approved disposable respirators (sometimes referred to as “dust masks”).

Gases and vapors are molecules and cannot be physically filtered. A barrier which keeps molecules of harmful gas from passing through will also keep molecules of oxygen from passing through, and you kind of need oxygen to live. In these cases, you need a respirator with a chemical cartridge. A chemical cartridge will either capture and hold the harmful molecules or chemically react to transform them into something less harmful. One of the earliest substances to be used in this manner is activated charcoal, which is still relied upon for filtering many kinds of chemicals. Your Brita filter uses activated charcoal to filter your tap water.

There is no single type of chemical respirator cartridge which will filter out every kind of gas or vapor found in prop making. It is absolutely vital that you know and understand what kinds of chemicals you are working with and what physical forms they are in so you can choose the correct type of respirator and cartridge to wear. As with particles, wearing a respirator makes your lungs take bigger and deeper breaths to compensate for the reduced flow of oxygen; wearing the wrong kind of respirator means you are taking bigger and deeper breaths of a toxic substance than you would wearing nothing. Some chemicals cannot be filtered by any type of cartridge and require either a supplied-air or self-contained breathing apparatus.

In any case, proper ventilation in your shop is still your best defense against airborne chemicals.