Prof Krishna's Answer Box

If you have any questions or comments to post in response to any of the topics discussed below, or something new, please send me an e-mail (safety@profkrishna.com)
I will answer it (if I can) or I will find out and respond. If I consider the question or comment sufficiently interesting to a large number of viewers, I may post question and answer here, with only last name initial of the questioner.

22 Dec 2011

You keep emphasising that Asians should not carry (especially lifting from a bent position) more than abaout 25kg.
(a) Why haven't we been told about it (in Singapore)?
(b) What we can do about it here, apart from ordering it from Australia at great expense?

(a) Yes you have been told about it, at least as a recommendation. Check the following out:


10 Feb 2009


Can you give us any guidance for lifting of persons by means of cranes beyond what is provided by Singapore's CP63?


1. From OSHA (USA)
This change to the correct URL was informed to me by Ranelyn Cabrigas, Social Media Manager, Atlantic Training LLC, Email: rcabrigas@atlantictraining.com. Thanks!]


2. From Construction Forestry Mining Energy Union (Australia)

3. From Washington State Legislture (USA)

4. From California State Goverrnment (USA)

5. From "Lifting World - The world famous Lifting World web forums" (EUROPE)


Firm guidance on the design and use of man-baskets suspended from cranes comes with the publication of EN 14502-1 Cranes – Equipment for lifting persons - Part 1: Suspended Baskets. This European Standard was approved by CEN on 25 May 2005 and will be published by BSI within the next few weeks. The new standard has not been mandated under the Machinery Directive, which means that it takes the form of guidance rather than a legally binding document. However, anyone facing a law suit will be in a weak position if they have not adhered to published best practice,

Which the standard represents. Nor does the standard take precedence over national laws governing the use of man-baskets on cranes (France, for example, takes a much stronger line than the UK against the practice). Among the demands of EN 14502-1for the design of baskets are the following key points: Suspended baskets shall be incombustible and protected against corrosion. The basket shall have a minimum freestanding height of two metres. When the suspended basket is designed to be used in situations where falling objects may be a hazard, the basket shall have a roof, able to withstand the impact of a steel ball weighing 7kg, falling from a height of two metres. When calculating the rated capacity, the weight of each person shall betaken as at least 80kg plus at least40kg of equipment for each person .A safety factor of at least two must be used in design calculations. The basket must be attached to the crane hook with either steel wire rope slings according to EN 13414-1or chains according to EN 818-4with a safety factor of at least: eight for chains, and 10 for wire ropes, including the end termination. The slings shall be fitted to the basket in such a way that they can only be removed with tools. The vertical distance between the floor of the basket and the crane hook shall be no more that three metres. The floor of the basket shall be secured to the frame by welding or some other equally effective means. The floor must be slip resistant and have drainage.

Free space on the floor shall be at least 600mm x 600mm for one person, and at least 400mm x 400mm more for each additional person. Suspended baskets must be designed so that if a load 1.5 times the rated capacity is applied at the worst position on the floor, any resulting inclination shall not exceed 20°.

Any gate shall not open outwards and shall have an automatic catch to prevent it from being opened inadvertently. Baskets shall have anchorage points in accordance with EN 795 for personal protective equipment and people in the basket shall wear a harness with lanyard. The standard also sets out detailed requirements for handrails and contents of the instruction manual.

The manual must state that the suspended basket shall only be used in combination with cranes, which are designed for the lifting of persons. The only clue as to which cranes are considered" designed for the lifting of persons" comes with the proviso that cranes must have powered lowering and not free-fall winches.

The manual must also state that: The crane and the suspended basket shall only be operated by people trained in the safe use of the combination, including the operating procedures for egress in case of power supply failure or control failure.

A crane driver should always be present at the normal crane control station when the basket is occupied.

Visible and audible communication should exist between the persons in the basket and the crane driver at all times during the lifting operation. The required equipment necessary to perform an emergency rescue shall be available throughout the lifting operation. During operation the employer should not require the crane driver and signaller to do other work at the same time, or direct a second crane and/or Basket.

Lifting slings for suspended baskets should not be used for any other purpose. Suspended baskets should not be used in wind in excess of 7m/s (25km/h), electric storms, ice, snow, fog, sleet, or other adverse weather conditions that could affect the safety of personnel. Machines, which can be operated simultaneously in the same place with risks of collision, should be stopped. Unintended movement of the basket should, where possible, be prevented e.g. by means of guide ropes or anchoring.

The suspended baskets, hook, catch, and fixed load lifting attachment should be inspected prior to each use. The hook must have a safety catch .The basket shall be positioned on a firm surface when entering or exiting. The lifting and supporting should be made under controlled conditions and under the direction of one appointed person.

6 Oct 2006

"Is there an easy way to visualise the various categories of risks after we have done the assessment, and also what we should do with them? "

I think of the risk space as a work area, with a floor and a ceiling. (See Figure at right.)

Events below the floor are"Low" risk, trivial, not worth spending time, effort and money on, althought they will need watching.

Events above the ceiling are "High" risk, catastrophic, more than I can afford, beyond which it is too risky to venture, although someone will have to try to reduce the risks to affordable ones.

In between are the "Medium" risks of direct concern, tolerable, and to be managed according to the hierarchy of risk controls, in a prioritised fashion.

15 Aug. 2006


Mr. T., a participant in one of my Hazard Evaluation and Risk Analysis courses, asks:

"In MOM's published Risk Management Guidelines, in assessing severity, it says that we should not consider the existing controls. It seems very unrealistic if we ignore existing controls in assessing the severity because the existing mitigation can be such that it actually lowers the severity and not just the likelihood." 


1. With the exception of highly specialized processes under strict quality control, Risk Assessment (RA) for the most part is quite subjective and qualitative. Hence, various paths exist to achieve the goal of risk assessment and management.

2. There is no right or wrong way to do RA. But all procedures must include: (a) Hazard identification (HI), (b) Likelihood and consequence evaluation, (c) Risk estimation, and (d) Risk control. Certainly, by the time one reaches step (d), existing controls (EC) must be taken into consideration before the residual risks are determined and controls implemented.

3. The question is when the EC are recognized and accounted for. This too is a subjective matter, depending on various factors such as nature of activity, experience and expertise available, and regulations governing it.

4. In practice, EC can be considered at any one of three stages:
(a) BEFORE RA: Consider EC right after HI. This is the most common practice. (However, the two steps should preferably be not combined, but EC to be done after HI.)
(b) DURING RA: Consider EC while assessing likelihood and severity, recording the corresponding levels with the EC in place. Here arises another question: EC for likelihood or severity?
In MOM’s Guidebook, it says: “As the severity of the hazard refers to the intrinsic or inherent nature of the adverse effect (eg. cancer, amputation or fatal injury) that may result from the hazard, it does not depend on the controls in place. Therefore, in assigning the severity level, the existing controls should not be taken into account.”
This is indeed the proper view according to the definition of severity evaluation as the consequence if and when the hazard is realized into risk, such as when a construction worker actually falls from height, or when a factory worker inhales toxic fumes. Any safeguards provided usually reduce only the likelihood of the risk, rarely the severity.
MOM’s Guidelines do not really forbid anyone from using existing controls that actually mitigate severity. For me to react more definitively to your question, I would like to see one example from you where you believe that existing controls actually reduce the severity itself.
If you can actually show that an existing control reduces severity, then it will certainly be accepted as a mitigating factor.
One example I can think of is a flu vaccination. The existing control of vaccination may reduce the likelihood of getting flu from high to medium, but it will also certainly reduce the severity of the flu from high to low if and when the person gets it.

[QUESTION to readers: How about netting or air-bags around scaffolding as severity-reducing existing controls? Comment, please!]

(c) AFTER RA: Consider EC after doing the RA. Then check if and how much the EC reduce the risk level.

5. It is more important to account for EC at some stage, in such a way that unnecessary time and effort are not wasted in evaluating risks which are well-known and controls for which are commonly implemented, usually mandated by authority.It is also critical to check whether the existing controls perform as planned, and whether they are being adopted by the workers as expected.