The physics of the Chernobyl accident

My latest book, an attempt to explain the Chernobyl accident to people who know a bit about physics but not a lot, placing it between the many accounts that have concentrated on the human story and some very technical reports, is now available on amazon after a professional work over by Art Works who have greatly improved the layout and type setting.

Find it at

What do we know about Covid-19?

Since everybody seems to be writing about Covid-19 I thought I should as well.

Update.  There is now a cacophony of Covid-19 writing. I'm not even going to try to stay up to date, let alone write anything more.

COVID-19 is the illness seen in people infected with a new strain of coronavirus not previously seen in humans. On 31st December 2019, Chinese authorities notified the World Health Organisation (WHO) of an outbreak of pneumonia in Wuhan City, which was later classified as a new disease: COVID-19. Based on current evidence, the main symptoms of COVID-19 are a cough, a high temperature and, in severe cases, shortness of breath.

On 30th January 2020, the WHO declared the outbreak of COVID-19 a “Public Health Emergency of International Concern”.

COVID-19 is now classified as an airborne high consequence infectious disease (HCID) in the UK.

Situation reports are available from:

Printed situation reports (worldwide – WHO) are available from:

The world situation can be monitored at

UK Government latest information and advice is available from:

The numbers of confirmed cases in the UK is going to be published daily at 2pm each day on

The table above is from 6/3/20

The Government also maintain a site giving updates on Covid-19: epidemiology, virology and clinical features.

On 30/1/2020 the government raised the UK risk level from low to moderate.


It is not yet clear how this virus will spread and the impact it will have. However, as of 4th March 2020 it is spreading widely across the world and there appears to be an exponentially increasing number of cases in the UK. Business have been advised to plan for 20% absenteeism at the peak.

The government summary of what is known about the virus may be a bit out of date – this is a fast moving event. It does say that “Although evidence is still emerging, information to date indicates human-to-human transmission is occurring. Hence, precautions to prevent human-to-human transmission are appropriate for both suspected and confirmed cases” and “We do not know the routes of transmission of COVID-19; however, other coronaviruses are mainly transmitted by large respiratory droplets and direct or indirect contact with infected secretions. In addition to respiratory secretions, other coronaviruses have been detected in blood, faeces and urine.”

“Fever, cough or chest tightness, and dyspnoea are the main symptoms reported. While most patients have a mild illness, severe cases are also being reported, some of whom require intensive care.”

When you have dyspnea, you might feel:

  • Out of breath,
  • Tightness in your chest
  • Hungry for air (you might hear this called air hunger)
  • Unable to breathe deeply
  • Like you can’t breathe (suffocation)

As of 3 March, a total of 13,911 people have been tested in the UK, of which 13,860 were confirmed negative. 51 were confirmed as positive (up to 85 on the 4th March).

We might expect the number of cases to rise rapidly over a period and then start to drop. The peak intensity and the duration of the disruption is hard to predict. The “social distancing” strategy is intended to reduce the height of the peak but at the expense of increasing the duration. There is a distinct possibility of repeat outbreaks in subsequent years, although these days we can hope that a vaccine will be developed. Each wave can have different inflection rates and different fatality rates. The figure below shows the 3 different waves of illness in the USA during the 1918 flu pandemic.


Figure ref < here>

Government Strategy

( 1st March)

Every government department to have a designated ministerial virus lead to help oversee government response to the global threat of COVID-19

Cross-government ‘war room’ of communications experts and scientists also set up ahead of public information blitz in coming weeks

Further COBRs planned this week, with ministerial COBR meetings upgraded to be held more frequently, if required.

The overall phases of the Government plan to respond to COVID-19 are:

  • Contain: detect early cases, follow up close contacts, and prevent the disease taking hold in this country for as long as is reasonably possible
  • Delay: slow the spread in this country, if it does take hold, lowering the peak impact and pushing it away from the winter season
  • Research: better understand the virus and the actions that will lessen its effect on the UK population; innovate responses including diagnostics, drugs and vaccines; use the evidence to inform the development of the most effective models of care
  • Mitigate: provide the best care possible for people who become ill, support hospitals to maintain essential services and ensure ongoing support for people ill in the community to minimise the overall impact of the disease on society, public services and on the economy.


These phase may have run its course with an increasing number of cases confirmed in the UK. (At this stage care is needed when interpreting the rise in confirmed cases. It may be more representative of the rise in testing rather the rise in cases).


The delay phase of the response will probably be based on public information campaigns urging hygiene, social distancing and recognition of symptoms. The intention is a lower the peak incident rate but probably at the cost of prolonging the course of the epidemic.

The government concern about planning for this stage is that the proposed actions have a social impact (and an economic one).

The company would probably prefer a longer duration, relatively shallow event rather than a shorter, sharper one that compromises site safety by having too many people off at once. At company efforts should focus on delay, at least initially.


For an operational site or company the mitigate stage is about maintaining site safety at all times and remaining fleet of foot to achieve what production is possible.

What happens when you have a suspect carrier on site?

For contacts of a suspected case in the workplace, no restrictions or special control measures are required while laboratory test results for COVID19 are awaited. In particular, there is no need to close the workplace or send other staff home at this point. Most possible cases [currently] turn out to be negative. Therefore, until the outcome of test results is known there is no action that the workplace needs to take. (COVID-19: guidance for employers and businesses).

The Company should consider implementing a policy of “social distancing” and added cleaning.

If it is confirmed that a carrier has been on site the PHE will carry out a risk assessment and give advice to the management (We can imagine that this will only continue to happen if the number of cases remains low).

Self-certification and isolation advice

The self-isolation advice given by NHS-UK is

If there’s a chance you could have coronavirus, you may be asked to stay away from other people (self-isolate).

This means you should:

  • stay at home
  • not go to work, school or public places
  • not use public transport or taxis
  • ask friends, family members or delivery services to do errands for you
  • try to avoid visitors to your home – it’s OK for friends, family or delivery drivers to drop off food

You may need to do this for up to 14 days to help reduce the possible spread of infection.

Home isolation advice can be found at: and for sharing a house with someone in home isolation at

By law, medical evidence is not required for the first 7 days of sickness. After 7 days, it is for the employer to determine what evidence they require, if any, from the employee. (A) Any company should agree and promulgate its policy for sick pay if the virus hits.

Employees may be advised to isolate themselves and not to work in contact with other people by NHS 111 or PHE if they are a carrier of, or have been in contact with, an infectious or contagious disease, such as COVID-19. (A) Again any company needs clear guidance on behaviour and pay under these circumstances.

Office cleaning

Coronavirus symptoms are similar to a flu-like illness and include cough, fever, or shortness of breath. Once symptomatic, all surfaces that the person has come into contact with must be cleaned including:

  • all surfaces and objects which are visibly contaminated with body fluids
  • all potentially contaminated high-contact areas such as toilets, door handles, telephones

Public areas where a symptomatic individual has passed through and spent minimal time in (such as corridors) but which are not visibly contaminated with body fluids do not need to be specially cleaned and disinfected.

If a person becomes ill in a shared space, these should be cleaned using disposable cloths and household detergents, according to current recommended workplace legislation and practice.

Guidance to the cleaners about personnel protective equipment (water proof gloves) and cleaning chemicals to use when cleaning potentially contaminated areas should be clear and transparent. (A) Write and promulgate enhanced cleaning regime for shared areas and for areas that might be infected.

All waste that has been in contact with the individual, including used tissues, and masks if used, should be put in a plastic rubbish bag and tied when full. The plastic bag should then be placed in a second bin bag and tied. It should be put in a safe place and marked for storage until the result is available. If the individual tests negative, this can be put in the normal waste.

Should the individual test positive, you will be instructed what to do with the waste.

How to protect your self

This section based on WHO advice

Wash your hands frequently

Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap and water.   Why? Washing your hands with soap and water or using alcohol-based hand rub kills viruses that may be on your hands.

How long any respiratory virus survives will depend on a number of factors, for example:

  • what surface the virus is on
  • whether it is exposed to sunlight
  • differences in temperature and humidity
  • exposure to cleaning products

Under most circumstances, the amount of infectious virus on any contaminated surfaces is likely to have decreased significantly by 72 hours.

Once similar viruses are transferred to hands, they survive for very short lengths of time. Regular cleaning of frequently touched hard surfaces and hands will, therefore, help to reduce the risk of infection.

Maintain social distancing

Maintain at least 1 metre (3 feet) distance between yourself and anyone who is coughing or sneezing. Why? When someone coughs or sneezes they spray small liquid droplets from their nose or mouth which may contain virus. If you are too close, you can breathe in the droplets, including the COVID-19 virus if the person coughing has the disease.

Avoid touching eyes, nose and mouth

Why? Hands touch many surfaces and can pick up viruses. Once contaminated, hands can transfer the virus to your eyes, nose or mouth. From there, the virus can enter your body and can make you sick.

Practice respiratory hygiene

Make sure you, and the people around you, follow good respiratory hygiene. This means covering your mouth and nose with your bent elbow or tissue when you cough or sneeze. Then dispose of the used tissue immediately.

Why? Droplets spread virus. By following good respiratory hygiene you protect the people around you from viruses such as cold, flu and COVID-19.

If you have fever, cough and difficulty breathing, seek medical care early

Stay home if you feel unwell. If you have a fever, cough and difficulty breathing, seek medical attention and call in advance. Follow the directions of your local health authority.

Why? National and local authorities will have the most up to date information on the situation in your area. Calling in advance will allow your health care provider to quickly direct you to the right health facility. This will also protect you and help prevent spread of viruses and other infections.

Stay informed and follow advice given by your healthcare provider

Stay informed on the latest developments about COVID-19. Follow advice given by your healthcare provider, your national and local public health authority or your employer on how to protect yourself and others from COVID-19.

Why? National and local authorities will have the most up to date information on whether COVID-19 is spreading in your area. They are best placed to advise on what people in your area should be doing to protect themselves.


Despite a further review of all the available evidence up to 30 November 2012 there is still limited evidence to suggest that use of face masks and/or respirators in health care setting can provide significant protection against infection with influenza when in close contact with infected patients. The effectiveness of masks and respirators is likely to be linked to consistent, correct usage and compliance; this remains a major challenge – both in the context of a formal study and in everyday practice. (

Employees are not recommended to wear facemasks (also known as surgical masks or respirators) to protect against the virus. Facemasks are only recommended to be worn by symptomatic individuals (advised by a healthcare worker) to reduce the risk of transmitting the infection to other people. (COVID-19: guidance for employers and business