Is mixing concrete dangerous, and what moving it into a cab takes away

Mixing concrete by hand carries hazards that a national safety authority has set out in print, so the question does not have to be argued from first principles. The UK Health and Safety Executive's construction information sheet on cement states that cement causes ill health mainly by three routes: skin contact, inhalation of dust, and manual handling. On the first it is specific. Wet cement can cause burns, and the sheet says the principal cause is thought to be the alkalinity of the wet cement: "If wet cement becomes trapped against the skin, for example by kneeling in it or if cement falls into a boot or glove, a serious burn or ulcer can rapidly develop." Those burns, it says, often take months to heal, and in extreme cases need skin grafts or can even lead to amputation. A splash can cause serious chemical burns to the eyes.

The second route is slower and more common. The sheet describes two mechanisms of cement dermatitis — irritancy, from the fine particles abrading the skin, and allergy, from sensitisation to the hexavalent chromium present in cement. It states that research has shown between 5% and 10% of construction workers may be sensitised to cement, and that plasterers, concreters and bricklayers are particularly at risk. Once someone has become sensitised to hexavalent chromium, the sheet says, any future exposure may trigger dermatitis, and some skilled tradesmen have been forced to change their trade because of this. Irritant dermatitis will usually clear up with treatment, it adds, but exposure continued over a longer period makes the condition worse and leaves the person more susceptible to the allergic form. It also notes that the longer cement is left on the skin through a working day rather than being washed off at intervals, the greater the risk of sensitisation becomes.

On dust the sheet is narrower than the internet usually is. High levels are produced when cement is handled, for example when emptying or disposing of bags, and in the short term that dust irritates the nose and throat. It attributes silica-bearing dust to scabbling and concrete cutting, makes no silica claim about mixing at all, and sends the reader to a separate sheet, CIS36 (rev1), for silica. We keep that line where the sheet draws it, although the looser version of it would suit this page better. The third route is the one nobody records as an injury: sprains and strains, particularly to the back, arms and shoulders, from lifting and carrying cement bags and mixing mortar. Its stated control is to avoid manual handling of heavy loads where possible and, in particular, to have cement supplied in 25 kg bags or ordered in bulk.

All three routes converge on one place: the ground beside the heap. Sand and aggregate are shovelled into a gauge box or onto a board. Cement bags are carried to that point, split and tipped. Water is carried in buckets and judged by eye. The mix is turned by hand with a shovel, and the finished concrete is lifted again, into barrows or headpans, and carried to the form. Every step is a manual handling operation, every step puts a person within arm's length of dry cement dust, and the last two put wet cement on boots, gloves and knees. That is a description of which tasks put skin, lungs and backs where the hazard sheet says the harm occurs, not an argument about productivity. We state no crew number, because our records hold no figure for how many people the operation takes, or for how many a machine replaces.

The first thing the machine changes is who lifts the aggregate. Across the six mixers in our catalogue the loading method is recorded as a self-loading bucket, checked model by model rather than asserted for the category, and one plant's configuration list names the arrangement in full: a hydraulically controlled front-load, rear-discharge bucket. The bucket takes sand and stone from the stockpile into the drum, which removes the shovelling and the barrow run on the feed side of the operation. On the discharge side the drum lifts and rotates through 270 degrees on five of those six, so a load is put where the machine can reach the form rather than carried the last stretch by hand. Only one of the six has a model page on this site; the other five are held back because required plant figures — engine, weight, overall dimensions, drum volume — are still unverified.

Proportioning is the judgement the machine does not make for you. Electronic hydraulic weighing is listed as an option on five of the six mixers in our catalogue and does not appear on the sixth at all. On one of those five it is also listed as standard, which contradicts the option line beside it, and we have not settled which is right: that machine's configuration list from the plant does carry a weighing unit, so the likelihood is that the option line is a range-wide template. A likelihood is not a specification, and this one is worth having in writing before an order rather than after it. Where weighing is not fitted, quantities are judged as they are judged on the ground, by eye and by the bucket. The machine has moved where the material is lifted from, not who decides how much of it goes in.

Cement is where this argument has to stop. A cement hopper appears as an option on five of the six mixers in our catalogue, never as standard, and we hold no description of how that hopper is filled. On the evidence in our own files somebody is still carrying bags, splitting them and tipping them, which is the exact task the hazard sheet names for both the dust route and the manual handling route. That is the distance between a machine that loads itself and an operation that no longer handles cement by hand. If bag handling is what you are trying to get rid of, settle before ordering what the hopper holds, at what height it is charged, and whether bulk supply can reach the site. None of those three has an answer in our records today.

Water arrives through the machine on most of what we hold, rather than in buckets carried to the drum. Our records cover sixteen self-loading mixers, and counting the plants' own configuration lists across them: an automatic water-fill controller on seven, an external suction water pump on the same seven, and a high-capacity water tank with self-priming system on eight — fifteen of the sixteen carrying some form of on-board water supply. The sixteenth has a configuration list that is unverified apart from a single entry, so it is a gap in what we know rather than a machine known to lack the equipment. The five crawler dozers in the same records have no configuration list and mix nothing, which is a difference of category and not a missing figure. So the figure to hold on to is fifteen mixers of sixteen, with one unknown, and five machines the question does not apply to at all.

On the six mixers in the catalogue, the controller and the suction pump are standard on five. The sixth is not an exception so much as a different description: its standard list carries a high-capacity water tank with self-priming system instead, which is the same job worded another way. One inconsistency in our own material belongs here. A photograph caption on our home page calls the external suction pump the option that lets the machine draw its own water on site, while the equipment data records it as standard on five of the six. The two do not agree, the equipment data is the one that came from a plant, and the caption is wrong rather than merely loose. It is being corrected instead of left where a reader can find it.

Judging a mix means looking into the drum, and where the operator stands to do it is a design decision. Of the sixteen mixers in our records, seven have a configuration list naming a camera, described in the plant's own wording as reversing and drum monitoring. Eight more name a high-definition LCD driving display and name no camera at all, and a display is not a drum view unless something is feeding it, so we count those eight as a screen in the cab and nothing more. That is fifteen mixers with something in front of the driver and seven with a stated view of the drum. On the six mixers in the catalogue, a camera system for reversing and drum monitoring is standard on five; the sixth carries the driving display instead.

What that changes is a position, not a hazard class. Cement is exactly as caustic whether the operator is beside the drum mouth or in a seat, and a camera adds no protection to anyone standing at the opening. What it removes is the reason to be there: on a machine with the drum view, the check that would otherwise be made over the rim is made from the cab. That is worth stating narrowly, because it is the whole of the claim. It is a change in where a person has to stand to do a job, and nothing beyond that. We hold no study showing it changes any injury outcome. Nor does an equipment entry tell you how good the view is in dust, in rain or after dark, which is a question for a demonstration rather than for a specification sheet.

Placing, screeding and finishing stay on the ground, and they are where wet concrete meets people. Our own photographs say so: one shows poker vibrators through a slab minutes behind the discharge, another shows five men spreading a slab by hand. Both are hand operations, and both begin after the load has left the drum. The sentence about wet cement trapped against the skin by kneeling in it describes those men precisely, and it describes them whether the concrete was turned with a shovel on a board or discharged from a drum. The same sheet also warns that gloves are not a clean answer, because cement trapped against the skin inside a glove can itself cause a cement burn. Nothing in a self-loading mixer's equipment list touches any of this, and nothing on this page tells anybody what to wear.

Two further things the machine does not do. It is not a washing facility: a high-pressure wash-down pump is listed as an option on five of the six mixers in our catalogue, and what it washes is the machine. One control the sheet names for cement dermatitis is washing the skin with warm water and soap at sinks large enough for the forearms, with hot and cold running water — that is site welfare, and it is unaffected by which machine is parked on the job. Nor does the machine reverse the dust decision. The sheet's first line of control for cement dust is to eliminate exposure where possible, "for example, by purchasing ready mixed concrete". A self-loading mixer is the opposite decision, taken because no batching plant is in reach or because a truck and pump cannot get to the pour, and the bags still get opened.

No injury statistic, incident rate or accident-reduction claim appears here, and that is a decision rather than an oversight. We hold no such data: we have run no study, we have no customer incident reports, and we would be the wrong source even if we did, because the party selling the machine is not the party whose count of injuries anyone should rely on. A page that told you this machine reduces accidents by some percentage would be a page that invented the percentage, and you would have no way to tell that from reading it. What a supplier can honestly do is name mechanisms, count machines, and stop there. Whether what the machine moves adds up to a safer job on your site is a judgement about your site, better made from the equipment lists above than from an adjective of ours.