MoD Health & Safety Handbook 

JSP 375 Vol 2 

`Sen' Notation 

13  Some substances are capable of causing respiratory sensitisation.  This means that they may 

cause people to develop occupational asthma.  Certain categories of respiratory sensitisers have been 

assigned the  Sen  notation in EH40, indicating the need for very careful control of exposure.  Health 

surveillance is appropriate for all employees exposed to respiratory sensitisers unless there is unlikely to 

be a risk of sensitisation under the conditions of use. 

14  Lead has OELs and asbestos has control limits and action levels, all of which are quoted in EH40.  

(See relevant leaflets) 

METHODS OF CONTROLLING EXPOSURE 

15  If it is necessary to control exposure (because prevention is not practicable), it is more effective to 

do this by process related means (changing aspects of the process or using engineering controls) rather 

than by methods, which rely on personnel (e.g. personal protection). A series of 3 flowcharts supporting 

the following guidance are given at Figures 1 to 3 below. 

Process related methods 

16 These 

may 

include: 

16.1 

Substitution   use a different form of the same substance (e.g. purchase of solution rather 

than preparation from a powder, use of pellets rather than a powder). 

16.2 

Specify maximum acceptable concentration of impurities (e.g. free crystalline silica in 

refractory materials and cements, n hexane in some solvents).  Advice on this may be obtained 

from manufacturers, technical sponsors and health and safety advisers. 

16.3 

Totally enclose the process, preferably keeping it under slight negative pressure (e.g. 

glove boxes, shot blast cabinets).  Alternatively provide the operators with a clean control room, to 

separate them from the hazard.  Biological agents should be controlled by reference to 

Containment Levels.  

16.4 

Use plant, processes or systems of work, which minimise the generation of hazardous 

substances.  There are many examples of this, such as brush painting instead of spray painting, 

floating plastic balls (croffles) on top of liquid treatment tanks to reduce evaporation, use minimum 

quantities, replace lids on tins.  Dust free cleaning methods should be used (never use 

compressed air, use a vacuum cleaner or wet methods instead of dry sweeping).  Safe storage 

should also be provided for hazardous substances and waste products. 

16.5  Partial enclosure with Local Exhaust Ventilation (LEV) (e.g. fume cupboards, 

microbiological safety cabinets). 

16.6 

LEV.  This may be fixed to a machine (e.g. lip ventilation at tanks, LEV at woodworking 

machines) or under the control of the operator (e.g. welding fume controls).  If LEV is to work 

effectively, it must be designed correctly.  This often means that specialist advice should be 

obtained from an occupational hygienist or environmental health officer regarding the general 

design, the air velocity required and the requirement for make up air.  When using adjustable LEV 

(e.g. when welding), the standard of control of the contaminant will depend on the user positioning 

the exhaust inlet correctly.  LEV must also be checked frequently and maintained, examined and 

tested regularly.  See paras 21 25. 

Leaflet 5 Annex G 

April 2003 

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