A compromise of many elements
This is not a rigorous treatise on chemical protection, but a broad overview, based on principles – for an international audience – and our experiences.
Chemicals are everywhere. We are made of them, eat, breathe, excrete, work and play with them – not necessarily in that order.
Just about every chemical can cause harm if there is enough of it. They may also cause damage to property, e.g. impressive explosions or fire, or to the environment – that just means killing things other than humans first, but ultimately it comes back to humans because, except for academics and astronauts, we all live on the same planet.
Aside from things like simple asphyxiants that displace breathable air, chemicals have to get through your own body’s defensive barriers in sufficient quantities to harm you. The likelihood, extent and nature of the harm are therefore influenced by many factors. For example, chemical properties (reactivity or mode of action), physical properties (form, volatility, dustiness), how it enters the body (the lungs are considered especially vulnerable), concentration, for how long you are exposed and how frequently, whether people hate you (and who might want to harm you), what other chemicals you are being exposed to, any existing ill-health conditions you might already have, and so on. The list is endless, but some elements are obviously more significant than others.
Eating hazardous chemicals is not usually a significant cause of ill health at work – that’s more what people do in their leisure time. It’s called junk food. This route is only significant when you work with highly toxic chemicals, e.g. small amounts can make you very ill. Aside from wearing a whole body suit, personal hygiene (washing) and prohibiting eating/drinking/smoking while working with chemicals are important precautions here.
The beautiful people on the planet already know the importance of good skin. Intact skin is surprisingly good at keeping stuff out. The lungs, with their specialised, thin lining are somewhat more vulnerable to attack. In this article, we’ll focus on personal protection for skin, eyes and respiratory system.
Intelligent people have used a small fraction of their brain power to work out strategies to protect humans from chemicals. In recognition that efficacy varies, these strategies are formulated as hierarchies; that is, they rank the methods of managing the risk.
Because intelligent people rarely agree on anything they didn’t think of first, there are multiple hierarchies. Nearly always top of the list comes avoiding the chemical or task. We know that seems almost too obvious, but it’s worth considering.
After avoidance, substituting the chemical for something less harmful or in a different physical form is often suggested.
These are very much strategic decisions and they protect all workers. At the bottom of the list we usually find personal protective equipment (PPE) such as gloves, respiratory protective equipment or goggles. This is a less effective method because it only protects the person wearing it. In addition, PPE easily fails. For example, it has a limited use life, people might not maintain it or wear it properly, it’s uncomfortable and it’s tempting to remove when being worn for long periods.
In reality it’s not a case of just one method; a mixture of methods is nearly always required in practical situations. Despite PPE being at the bottom of the list, it is routinely used as supplementary protection.
A favourite of risk managers is getting someone else to do it. They call it risk transfer because, on paper, it becomes someone else’s problem. Pushing the problem onto someone else (like a toll manufacturer) does not mean it doesn’t have to be dealt with, however. It can even come back to bite you if you choose your transfer partner poorly.
Personal Protective Equipment
Skin and eye protection rely mainly on physical barriers, acting as a second, chemically resistant skin. Even if you haven’t worked in the chemical industry, this kind of protection is readily seen in hardware stores or in movies, especially the ones about pandemics, like Outbreak or Contagion.
We are all familiar with rubber gloves, aprons, PVC suits, rubber boots, goggles and visors – there is a surprising amount to consider in selecting the right protection. Pretty obviously, the first consideration is foreseeable exposure scenarios – this determines the type and extent of protection needed. Goggles and gloves will not stop splashes to the face, but then again, the eyes are far more sensitive than facial skin. Gloves will not protect much of the upper arms, whereas gauntlets will.
Beyond that, the materials from which the protection is made are of primary importance. More often than not, workplaces use mixtures of chemicals and this can make PPE selection more complicated.
Typically, gloves are made from PVC, latex, nitrile or neoprene. Although some specialised PVA and laminated composite gloves are also available, they are not as widely used. Latex gloves have been associated with allergic skin reactions, or dermatitis. Latex is a generic term, however, covering a range of natural and synthetic rubber sources and non-allergenic – or at least less allergenic – latex gloves are available.
It can come as a bit of a surprise to some people that solid objects are not as solid as they appear to be. Indeed, as chemical and atomic physicists have taught us, they mostly consist of nothing – people are charging you lots of money for nothing.
Substances will permeate through gloves; in short, they let stuff through to varying degrees. Just about any glove material will offer at least some protection against solid chemicals or water-based chemical solutions, but the same may not be the case against organic solvents like kerosine. These can cause some glove materials like latex to quickly degrade and fail in use.
There are a couple of related parameters used to assess glove material suitability:
• Permeation breakthrough time – This indicates how long it takes for a chemical to work its way all the way through the glove material from the outside, which obviously depends on glove thickness. You would not want to continue wearing a glove that had been fully permeated. The longer it takes, the better the protection
• Permeation rate – This is the maximum speed or flow rate; that is, the amount of chemical going through each cm2 section of surface per minute. These relate to immersing your gloved hand into a chemical bath and holding it there until it makes its way through the glove
• Degradation – This is assessed by the observer looking for things such as embrittlement or swelling, indicating imminent failure. There’s obviously little point in measuring permeation parameters if the glove is badly affected by the chemical
The test conditions may not relate to reality; they are extreme conditions. You might not normally have your gloved hand submerged for long periods, but some activities are similar, like painting, where the paint can be constantly dripping onto the glove from the brush. It might simply be that splash protection is all that is needed, however.
It’s rare for a single glove to offer very good protection for all chemicals in use in a workplace. It’s just not practical to change gloves every five minutes to get the highest protection for that specific chemical when you are dealing with different chemicals, risking contamination when removing each time. You can usually reach a pragmatic, compromise choice, however, which offers fair protection – at least splash protection – to most of the chemicals you are using.
So much for design and selection. Manufacturing can introduce defects, such as pinholes which may not be immediately apparent. That’s where manufacture to recognised standards and quality assurance come in – We knew there was a use for quality people somewhere.
Degree of fit and comfort needs to be considered too. Manufacturers produce a range of PPE sizes to fit most humans. Some glove materials are especially stretchy, so will conform to your shape, even if you have fat fingers. PVC suits only ever seem to come in one size – too big.
Selection must also consider durability. Thicker gloves offer more protection, all other things being equal, but at the cost of dexterity. Thin gloves offer excellent dexterity/feel but generally offer minimal mechanical resistance – they are easily torn.
If dexterity is very important, however, thin gloves are the answer, but factor in frequent replacements – disposables, in other words.
Other skin and eye protection
Many of the issues we’ve already considered for gloves – their chemical resistance, fit and comfort – are also very relevant for other forms of skin and eye protection. You may want to really get into the spirit of things and wear a gas tight suit for full protection, though they do make you look rather fat. I’ve been compiling a list of things you really shouldn’t do in a gas tight suit, either because it is unpleasant, dangerous or just doesn’t look good.
Getting people to wear PPE is another matter – and when they do wear it, getting them to use it properly is even harder. Getting them to discard it when it’s worn out – completely permeated with nasty chemicals, now held close to the skin in a nice warm sweaty environment – is harder still.
That’s where proper training, consultation and even user trials come in. Cost is obviously a factor whenever you invite the procurement manager to offer an opinion and this will start the debate as to whether it should be cheap single use disposables as opposed to more expensive but maintainable models. PPE maintenance often starts off with good intentions but fades into oblivion when someone has to do something.
Respiratory Protective Equipment
Clearly some of these issues also apply to respiratory protective equipment (RPE). RPE is widely used. In most workplaces it comes in the form of respirators. These use some method to filter contaminants to substantially reduce their concentration in the air that is breathed in.
If you like dressing up as a fireman, going down sewers or enjoy holidays in oxygen deficient atmospheres, you might instead wear breathing apparatus, which provides its own supply of uncontaminated air.
We’ll only consider respirators here. These come in two basic forms – those that rely on tight fitting over the nose and mouth and those that do not, like a hood or a powered helmet. Some are powered to reduce effort and others rely on the effort of the lungs to do their work; filters can offer quite a bit of resistance to breathing.
There’s a surprisingly wide range of vibrant colours, though they mostly come in white, blue or black. The filter may be integrated or separate, e.g. cartridges. Different filters can deal with dusts, aerosols or gases, or a combination of these. Choosing the right filter obviously matters. Some RPE neatly combines facial protection with an integrated visor.
Respirator performance is characterised by its protection factor (PF). This is the factor by which it reduces the contaminant – dust, aerosol, gas – concentration. It’s a relative term, a ratio, rather than absolute.
A PF of 10 means it will reduce the concentration by a factor of 10. So, if the contaminant is at a concentration of 200ppm, it will be reduced to 20ppm (a tenth) inside the respirator. Don’t you wish you’d paid attention to the mathematics teacher at school? The PF assumes the RPE is being worn correctly and is a good fit.
You can probably see where this is heading. Mostly you’ll want the concentration inside the mask to be below any applicable airborne exposure limit that may apply. That means that if you compare the likely concentration in the workplace with the recommended or legally applicable exposure limit, you can estimate the sort of PF that you’ll need. Sounds simple, doesn’t it?
PF isn’t the only consideration though. The effectiveness of RPE, just like with gloves, depends a good deal on whether it is being worn properly and whether it fits. For those who rely on tight fit, a leak around the face seal or a defective valve immediately compromises the respirator, rendering it useless. Hence, face-fit testing is routinely undertaken before you use a mask for the first time. This is to make sure you choose the right size for your face and know how to make sure it fits properly. This is supplemented with simple leak testing every time you wear it, as a final check that you’ve adjusted it correctly.
It depends on the job too. Massive cartridge respirators are all very well, but if the task means you constantly knock it and dislodge the face seal, then you might as well not bother.
Clear, wide vision and ability to communicate may also be important – respirators can muffle your voice and, added to a noisy environment, make it difficult to be understood.
If the job is very intensive, consider powered respirators which reduce breathing effort. The powered hood respirators – which do not rely on a tight fit – filter the surrounding air and blow it over the wearer’s face and breathing zone, having the side effect of a cooling action. As with skin or eye protection the final choice is often a compromise – a holistic, proportionate, pragmatic solution.
There are many methods that help protect you from chemicals. PPE helps but don’t ask it to do more than it can. It can only supplement other measures you are using. It’s dangerous to rely too heavily on it because it is easily foiled.
When specifying PPE, it’s not just about the performance of the kit itself. Take into account the job and especially human factors. Make sure you understand its limitations and those of the human wearing it.
Try wearing a PVC suit, full face respirator, rubber gloves and boots for 12 hours while doing a strenuous job and you’ll develop a new appreciation of why comfort and fit are important. You may also lose a little weight or get a fungal infection from excessive sweating. It’s nice to know there are still some simple pleasures in life.
Published: 18th Oct 2012 in Health and Safety Middle East