Ventilation

Ventilation is very important when you are working with chemicals.

If the ventilation system does not work properly, the following problems and illnesses can occur:

  • Irritation of air passages or other illnesses and problems caused by excessive concentrations of harmful substances (vapour and dust).
  • Problems and difficulties in concentrating in high temperatures.
  • Discomfort caused by low air exchange rates.

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The purpose of ventilation

The purpose of ventilation is to prevent problems and illness and to provide a reasonable indoor climate.
Ventilation in existing ships is often a complicated affair. This manual will therefore concentrate mostly on the defects and deficiencies that can occur in ventilation and local air extraction.

Ventilation problems

Short-circuiting between intake and exhaust air
This problem occurs especially if the air intake and the exhaust are wrongly positioned. The problem also becomes worse in unfavourable wind conditions. It is not unusual for exhaust gases from the ship's funnel to get sucked into crew accommodation. Increasing the height of the funnel or fitting a horizontal fin on the casing can often solve this problem.
Increasing the height of the funnel and/or mounting a horizontal fin on the casing can prevent smoke from the funnels being sucked into crew accommodation.

Noise and inaccurate temperature regulation
On many ships, inlet air has a constant temperature, while room temperature is adjusted using an airflow restrictor. This method is imprecise and creates varying degrees of pressure in the system, resulting in draughts and noise.
Pressure regulation using a frequency converter is a cheap and easy way of preventing draughts and noise, whereas other methods such as regulating valves provide a constant volume of air in the system. Otherwise, you can allow the excess air to be released by opening a valve in the ventilation room. The best method is zone heating in every room. This ensures the right room temperature with a constant volume of fresh air and valves can be removed.

Draughts
Draughts occur when there is an imbalance between the air extraction and inflow rates. So it is not enough to ensure extraction, sufficient incoming air must also be provided.
 

Conditions on the bridge
Large windows affect the temperature on the bridge, which means that a normal ventilation system is often insufficient. Small air-conditioning units (fan coils, split units) can be a solution but they should placed so that personnel do not suffer draughts from inflowing air. There can also be noise problems if insufficiently dimensioned.

Tobacco smoke/passive smoking
The Smokefree Environments Act 2007 states that smoking policies must the drawn up and that no-one should be exposed to passive smoking. Smoking rooms can be established and smoking in single berth cabins allowed (under certain conditions).

Maintenance
Ventilation systems must be properly maintained in order to work properly. Automation, components and manifolds should be routinely checked and cleaned. It is not enough just to change the filters. The filters used ought to be fine filters, at least type EU6.

Local extraction

Hot processes
In local extraction, it is important to identify the kind of pollutants to be extracted. If for example hot welding fume is being removed from a booth, the extraction point must be located higher than the welding unit and effective air suction must be generated between personnel and the extraction point. An extraction nozzle is recommended. Welding requires an extraction rate of 0.5-1.0 m/s. Use a hood for removing contaminants from hot ovens and hobs, etc., in the galley. Cooker hoods should remove the equivalent of about 1,000 m3/hour/metre. Large dishwashers should have extraction fitted directly to the machine.

Cold processes
For paint or other cold processes, use rear-edge extraction with an airflow rate of about 1,000 m3/hour/metre. A fume cupboard/hood is another solution. The air speed in the opening of the fume cupboard/ hood should be about 0.5 m/s. The speed can be measured with a rule, stopwatch and smoke pipette.

Hot and cold processes
A solution which can meet the need for both warm and cold processes is a Tornado extraction unit. This is an extractor canopy with an air inflow jet up the rear wall. For hot and cold processes in cleaning baths, the capture rate away from personnel must be 0.2-0-5 m/s.

Avoid draughts
When installing local extraction, replacement air should be provided without creating draughts. Draughts annoy people working there while also reducing effectiveness.
Sufficient replacement air must be supplied and the volume of inlet and exhaust air must be balanced.

Mobile extraction
Use mobile extraction equipment when working with harmful substances, gases and fumes elsewhere on the ship. Hoses allow exhaust air to be ejected into the fresh air. Consider the wind direction when positioning these hoses, as pressure from the wind can stop the air exhausting. There is no reason to direct the air over the ship itself, so position the hoses over the railing to leeward.See also Seahealth Denmark’s Sector Guidance No. 2 on local extraction.

Legislation

Mechanical extraction requirements and air replacement requirement
Danish Maritime Authority Notices B Ch II-4A – Designing and equipping working areas and workplaces. Technical Regulation no. 6 of 3rd July 1997 requires that mechanical extraction must be provided when handling paint etc. There is no indication of the volume of air and the method required but the intention is to remove the risk of harmful effects to safety and/or health from airborne particles, vapours and gases. Technical Regulation on working,No. 2 of 26th August 1996 also applies.

The Danish Maritime Authority’s technical regulation for ship building and equipment etc., lays down regulations for mechanical air exchange. These requirements ought to be taken into account when the ship is built as it is very difficult to improve this later.


Mobile extraction
Position hoses to leeward.

Senior Occupational Health Consultant

Anne L. Ries

alr@seahealth.dk

+45 3311 1833

+45 2961 8860

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