Author: Dean Burns / Editor: Adrian Boyle / Reviewer: Rebecca Ford / Codes: HAP11 / Published: 17/01/2018
Chemical incidents usually happen following leaks, explosions or fires in industrial settings. Most sites using chemicals are required to perform risk assessments and have plans to mitigate the effects accidental release. Terrorist use of chemical warfare agents is rare, but important, the Tokyo subway attacks with Sarin. Additionally more recently, Syria saw a chemical attack in 2017. The effects of poisoning may be acute, or may produce long lasting, chronic health effects that may carry a significant health burden .
Industrial chemical use in the UK is regulated by the Control of Major Hazards Regulations 2015 (COMAH) in which is enshrined the Seveso III directive from the EU2. Certain industries are reportable to COMAH, especially those using oil, gas, chemicals or explosives. Under COMAH, each company has a duty to have a major accident plan, and to be involved in surveillance. The European Major Accident Hazards Bureau (MAHB) has a database of all reportable incidents. The International Programme on Chemical Safety (IPCS) is a worldwide surveillance and information body run by the World Health Organisation (WHO).
HAZOPS is a risk assessment system that balances hazard and gain to a level known as As Low as Reasonably Practicable (ALARP). This is an acceptable standard in law. Risk assessment for industries takes into account:
- Centres of population
- Geographical factors such as watercourses and prevailing wind in the event of a plume.
The CCA (Civil contingencies Act 2004) moved responsibility for decontamination from the fire service to the health service, unless there are mass casualties involved. Each acute health trusts, must have a major incident plan that is regularly updated.
The priorities for the hospital response are
- Containment of the incident and prevention of secondary contamination
- Triage with basic first aid
- Decontamination where it has not taken place on scene
- Recognition of toxidromes and seeking of advice
- Appropriate treatment supportive or antidotal.
- Transfer to definitive treatment
- A safe end to the hospital response
- Continuation of business after the event
The chemical incident plan should be adapted to individual hospital configuration, but along the lines of the guidance from the Public Health England and Department of Health . There is also a close tie in with the hospital Major Incident plan, and many principles, such as recognition that there will be a police investigation afterwards, are the same.
According to the HSE who monitor COMAH reportable chemical incidents in England & Wales, there have been five major incidents involving hydrocarbons (eg propane); two involving petrol / oil and two involving cyanide compounds between 1999 and 20045. In 2005-2006, four major accidents in the UK were reported to the EC. Across Europe, the commonest incidents reported to MAHB involved Ammonia (72) or Hydrogen Chloride (63). Most chemical incidents involve unknown chemicals, or are too small to be reported.
Public Health England has a number of resources on specific chemicals available on their website, including toxicological data. Toxbase and National Poisons Information Units are also useful.
Hazchem (UK Hazard Identification System) is a UK system for managing chemicals and information. The most obvious manifestation are the boards carried by vehicles transporting chemicals which state the possible hazard (eg corrosive or flammable), the UN recognised product number for identification, emergency response codes for pre-hospital personnel and a 24 hour contact number for more information.
The following key points should be taken in a focused history
Exactly what exposed to and how much (ie volume and concentration)?
What protective measures were taken?
What treatment was given?
From these, the likely effects and time over which they should happen may be predicted. For all poisoned patients, once decontaminated, the focus is on resuscitation and support of vital functions. Most poisons do not have antidotes and so standard resuscitative principles will apply. The only exception is a known poisoning with paraquat where excess oxygen can increase long term pulmonary fibrosis however the patient should not be allowed to be excessively hypoxic as this too can be fatal.
Up to date information can be obtained from TOXBASE, the National Poisons Information Service and the Public Health England website. The information changes constantly, so it always worth checking.
Exposure is a function of the concentration of poison that the patient is exposed to, and time. The physicochemical properties of the substance (eg corrosive, lipid solubility, flammability) will determine likely effects, as will the route of exposure. Some chemicals are not absorbed through the skin, so a dermal exposure may have minimal effect compared to ingestion. Others, e.g. Hydrofluoric acid can exert major systemic effects from dermal exposure. Many incidents, particularly fires and explosions, will also produce either physical injuries that need treatment or inhalation of combustion products such as hydrogen cyanide or phosgene gas (from PVC).
The exact effect will depend on the exact chemical. It should be borne in mind that some chemicals do not exert their effect for some hours and observation may need to be prolonged (e.g. nitrogen dioxide which may not cause severe pulmonary oedema until 72 hours later). For most chemicals, the treatment should be supportive those which have recognised antidotes should be recognised. Departmental antidote stocks should be regularly checked to ensure they are in date and some, such as atropine and oximes, are available in pods which can be called upon in an emergency.
Exact symptoms will depend on the toxidrome of the chemical. Many chemical weapons are organophosphate based (eg Sarin or VX), and as there is an antidote, it is important it is recognised. The mnemonic SLUDGE may help for systemic symptoms, and patients characteristically have pinpoint pupils:
- GI Upset
For a severely poisoned patient, PPE may be required. The patients should be resuscitated and atropine given to a point where the pupils are just starting to dilate and bronchospasm stops. This may require repeating as the half-life of many organophosphates is longer than the Atropine pralidoxime has a longer time of effect and may be used.
The table below shows other toxidromes include (with antidote):
Normal pupils size, pink or cyanosed skin, decreased conscious level, decreased respiratory rate
Mydriasis, cyanosis, increased respiratory rate
Normal pupil size, cyanosis despite good oxygenation, decreased respiratory rate
Rapid onset severe pain and erythema
General principles of care of contamination
Contamination has three phases: 
Primary is from the incident and can only be minimised before the event (by safety measures, Personal Protective Equipment (PPE), handling plans etc).
Secondary comes from contaminated people leaving the scene and taking the chemical with them, and may occur from the exhalation of patients with certain poisonings, such as cyanide .
Tertiary results to the environment, including air and water-borne spread.
Bringing a patient who may have been contaminated into a department runs the risk of contaminating you, the Emergency Department and even the hospital. Other people in the waiting room may also be contaminated, and the department may become unusable. A patient arriving into the waiting room should be asked to wait outside and be spoken to and assessed at a safe distance. It can then be decided if they need decontamination. A second patient arriving with the same complaint requires the chemical plan to be activated, but dealing with the first patient should not be delayed. Once decontaminated, they can enter the department and be treated.
The important organisational concept is to have separate dirty and clean (or hot and cold ) areas  which are divided by a very definite line across which only the patient should pass once decontaminated. Staff performing the decontamination must be very aware of whether they are dirty or clean and stay that way until relieved or stood down.
Most chemical (70-85%)  can be removed by getting the patient to take off contaminated clothes these should be treated as hazardous waste. If a patient is contaminated with non-caustic chemicals they should undertake a process of dry decontamination which involves blotting and rubbing exposed skin gently with dry absorbent material such as blue roll and disrobing. All waste should be bagged for disposal. If the patient is exhibiting signs of contamination with caustic chemicals such as itching, redness of the skin or burning of the eyes, wet decontamination should be performed. The exceptions to this are chemicals such as Sodium which react violently with water. Acids or bases should never be neutralised with the opposite as this produces an exothermic reaction which could cause burns.
Healthcare staff safety is paramount, it is clearly undesirable to create further casualties by secondary contamination. In many plans, doctors do not need PPE as the chemicals do not cause secondary contamination e.g. chlorine.
If needed, PPE should be an all-in-one chemical-resistant overall  with integral head/visor and hands/feet worn with a respirator, gloves and boots. A respirator is a filter of varying gauge that allows breathing of external air. Breathing apparatus delivers piped or tanked air, and requires training. PPE is very hot and does not allow for manual dexterity: minimal treatment can therefore be provided while wearing it. Staff must be rotated regularly and frequently to avoid the inevitable fatigue which ensues.
- The department must be separated into a dirty and clean areas Grade C recommendation Level 5 evidence
- Removing clothes removes most chemicals Grade C recommendation Level 5 evidence
- Yamashita, Yamashita, Ando. A long-term follow-up of lung function in survivors of paraquat poisoning. Human & Experimental Toxicology (2000); 19: 99-103
- Health & Safety Executive: COMAH
- HPA: CBRN incidents: Clinical management & health protection September 2008.
- Department of Health Emergency Preparedness Division. The NHS Emergency Planning Guidance 2005
- Health & Safety Executive. COMAH accident reports.
- Major Accident Hazard Bureau personal communication
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- Okumura et al. Clinical review: Tokyo protecting the health care worker during a chemical mass casualty event: an important issue of continuing relevance. Critical Care 2005; 9:397-400
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