This is an appeal to others within my industry to think about how we might help with the global crisis caused by Covid-19. My business is spray nozzles. We supply nozzles to all kinds of industries for all kinds of applications. As a spray technology specialist I have watched with interest the various pictures of mass spraying going on in various cities around the world. As a European the use of such equipment seems very alien and draconian. Of course, people that live in areas of the world with endemic insect borne diseases will have seen this type of equipment being used in public places before many times.
Below are my initial thoughts on this as a spray nozzle specialist. I am not an expert in disease control or disinfecting though. Normally in business we tend to want to find out our own solutions to problems and then jealously guard them as a means to leverage competitive advantage. In this case, however, I’d like to share my initial thoughts in public and invite other experts to contribute towards a genuinely collaborative dialogue. I don’t know if the spray technology industry has a role to play in helping deal with all this, I suspect we might have a small contribution to make and this is what I’d like to explore in a public forum.
Initial thoughts
The large-scale public spraying that traditionally occurs is mainly for the control of insect disease vectors. So, this might be a good place to start. From a spraying perspective there are several differences between spraying for the control of pests such as mosquitos and spraying to combat a virus directly. We should look at the differences between insects and viruses and the chemicals used and maybe draw some conclusions as to the best type of spraying against coronavirus.
We might also look at the agricultural spraying sector, which involves large-scale spraying outside, for some suggestions. As with insect vector control, there are differences between crop spraying and disinfecting but crop spraying is still on a similar order of magnitude to what might be necessary for treating urban areas for coronavirus. So, there might be some lessons to learn from crop spraying.
Finally, we might look at the regular disinfecting spraying that goes on in specialist environments like hospitals. This is on a very small scale but there will be lessons to learn here as well, particularly with the efficacy of the chemicals used.
Large scale urban insect control
Residual spraying
Residual spraying involves the application of an insecticide to a surface. The residue will remain on the surface for days or weeks. If an insect lands on the surface it will receive a lethal dose of poison. This process relies on the insecticide being stable enough to last for a long period of time and for the spray to be delivered in such a way to form a coating that will last.
Fogging
The other method of insect vector control is to fog an area with an insecticide with the aim of killing airborne adult insects on contact. This method requires that a lethal dose of insecticide remains in the air long enough to come into contact with the insects.
This method relies on ultra-low volumes of insecticide with a very fine droplet size. These are distributed over a large area by blowing them with a fan. Atomisation can be achieved even at low fluid pressures by the use of strong air currents which also distribute the spray. The trick is to have the droplets very small so they remain airborne long enough to be effective. This type of spraying requires an understanding of insect behaviour as it is only effective when the insects are active.
What about coronavirus?
The coronavirus is spread by human to human contact or it can be picked up from surfaces that infected people have recently touched. The virus is not thought to be truly airborne. It is true that if an infected person sneezes then coronavirus carrying droplets will be in the air for a short period of time but this is measured in seconds rather than minutes. After a short period of time the air will be clear of pathogens but the sneezed droplets will settle on surfaces and remain viable for hours. This is unlike truly airborne viruses like measles which remain contagious in the air for hours. Walk into a lift an hour after someone infected with measles has been in it and you can catch it even if you don’t touch anything. This is why measles is one of the most infectious diseases known with an R factor of 15 in some outbreaks. Coronavirus is, thankfully, far less contagious primarily due to the fact that it is not truly airborne.
Initially it would seem that, when spraying to combat a virus that may be present on surfaces, we would need to emulate the surface contact spraying for insect vectors. However, after some thought this might not be best after all. Viruses and insects are very different beasts. With insects we need the poison to remain long enough on the surface for the insect to come into contact with it. This relies on the insect moving to the poison. A virus does not move and, as such, we need to achieve direct contact with the virus in much the same way as for airborne insect spraying.
Disinfecting agents won’t remain active for long. The bleaches that are effective against viruses are light chemicals which evaporate quickly. The insecticides used in residual spraying are formulated to remain stable and not evaporate so they remain on the surface for a long time. If we spray for coronavirus then we need to be destroying very quickly any viruses that are already on the surface i.e. before the disinfectant evaporates away. We also need this because bleaches and other disinfectants are dangerous to human health so, having them linger around for a long time is probably not a great idea.
Crop spraying
Spray penetration
Another factor to consider is the reach of the spray. With direct spraying from a normal hand-held sprayer we can get good contact with a surface in the direct line of sight of the spray but we get no contact with shadowed areas i.e. areas that are blocked form a direct line of sight. The trouble with many of our public places is that these shadowed areas are when humans tend to put their fingers. Think about the undersides of chair arm rests, under tables, all those little nooks and crannies that a stray finger might rest on. Getting to these areas with a standard direct spray might not be possible.
A fog or mist spray made of very fine droplets might stand a better chance of reaching all these areas. Furthermore, the fine distribution of droplets will mean that the dwell time of the spray in the environment is low; this would be a problem if we were trying to kill insects on surfaces but because the time for a bleach to kill a virus is more or less instant this type of spraying will remain effective for surface-dwelling viruses. As such the fine fogging systems might be a safer and more effective approach.
The benefit of very small droplets is well known in the agricultural sector. When spraying into thick foliage, for example coffee bushes, to treat with a fungicide the leaves in the interior of the plant need to be reached. Far better coverage is achieved with small droplets than with bigger ones. Whilst the urban jungle is somewhat different in topology the principle lesson may be the same.
Coverage
Another factor to consider is coverage. We are aiming to cover as much of the surface as possible. With direct spraying using a conventional flat fan spray nozzle we will get a good more or less 100% coverage. However, this will require a lot of spraying. If we are using misting or fogging systems then drop size becomes incredibly important. We can learn a lot from crop spraying testing. The photo below shows some splatter testing for various different spray types. The overall coverage of the paper by the spray is actually about the same in all four cases. However, the right hand example uses a large drop size spray and is dosed at 300 litres per hectare while the one on the left-hand side gives the same coverage but used 120 litres per hectare; this used a nebuliser sprayer with a much smaller droplet size.
The problem, however, is one of cost and delivery of the necessary equipment. Places with endemic insect borne diseases have this type of fogging equipment on hand. It can be repurposed easily enough for combatting coronavirus. In Europe, though, we do not have this sort of equipment readily available.
An appeal
I don’t actually have the answers as to which spraying system will best help in this crisis. The cynical part of me thinks that the photos of people mass spraying in hazmat suits using thermal foggers and other sci-fi looking spray technology is just for show. The government can be seen to be doing something “drastic” by this show of force, but the main effect is psychological rather than actually halting the spread of the virus.
But the more hopeful part of me wonders if our humble, niche industry of spray nozzles might have a small and genuinely useful part to play in dealing with all this. I’d invite anyone from the nozzle manufacturing or spray engineering industries to have an open discussion on this. The best way to spray will not involve any new proprietary spray nozzle technology, we will all have access to the correct product, I’m sure, but perhaps we should put aside competition and pool our knowledge to work together?
I also invite anyone with any relevant input from the chemical industry / cleaning sector to give input i.e. what should we actually be spraying? As I said at the start I’m not a chemist or an expert in disease control. This spraying application is not something that we have really seen in the UK before, especially in public places. Most of the advice I have seen seems to suggest that sodium hypochlorite solution or hydrogen peroxide solution would be best but there may well be better liquids to spray that are more effective.
How can we best collaborate to maybe find some answers?
Ivan Zytynski
Director
Spray People Group
